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251.

यदि `tan^(-1)""(4)/(3)=theta` तो , ` cos theta` का मान ज्ञात कीजिए ।

Answer» Correct Answer - `(5)/(sqrt(26))`
252.

सिद्ध कीजिए- `tan^(-1)""((cos x-sinx)/(cos x+ sinx ))=(pi)/(4)-x`

Answer» यहाँ `(cos x-sinx )/(cosx+sinx)=(cosx(1-(sinx)/(cosx)))/(cosx(1+(sinx)/(cosx)))=(1-tanx)/(1+tanx)=(1-tanx)/(1+1*tanx)`
`=(tan""(pi)/(4)-tanx)/(1+tan""(pi)/(4)tanx)=tan""((pi)/(4)-x)`
`:.` बायाँ पक्ष `= tan^(-1)""((cosx-sinx)/(cosx+sinx))`
` =tan^(-1)[tan""((pi)/(4)-x)]=(pi)/(4)-x=` दायाँ पक्ष
253.

सिद्ध कीजिए कि `tan^(-1)((cosx)/(1+sinx))=(pi)/(4)-(x)/(2)`

Answer» बायाँ पक्ष `tan^(-1)((cosx)/(1+sinx))=tan^(-1)[(sin((pi)/(2)-x))/(1+cos((pi)/(2)-x))]`
`=tan^(-1)[(2sin((pi)/(4)-(x)/(2))cos((pi)/(4)-(x)/(2)))/(2cos^(2)((pi)/(4)-(x)/(2)))]`
`=tan^(-1)[(sin((pi)/(4)-(x)/(2)))/(cos((pi)/(4)-(x)/(2)))]`
`=tan^(-1)[tan((pi)/(4)-(x)/(2))]=(pi)/(4)-(x)/(2)`
`impliestan^(-1)((cosx)/(1+sinx))=(pi)/(4)-(x)/(2)="दायाँ पक्ष "`
254.

सिद्ध कीजिए - `tan^(-1)[(sqrt(1+sinx)+sqrt(1-sinx))/(sqrt(1+sinx)-sqrt(1-sinx))]=(pi)/(2)-(x)/(2).`

Answer» [परिमेयीकरण करके हल कीजिए ]
255.

यदि `tan^(-1)x=theta" तो "sin^(-1)""(2x)/(1+x^(2))`का मान ज्ञात कीजिए।

Answer» `tan^(-1)x=theta`
`impliesx=tantheta`
अब `sin^(-1)""(2x)/(1+x^(2))=sin^(-1)""(2tantheta)/(1+tan^(2)theta)`
`=sin^(-1)(sin2theta)=2theta`
256.

सिद्ध कीजिए - `cot^(-1)[(sqrt(1+sinx)+sqrt(1-sinx))/(sqrt(1+sin x)-sqrt(1-sinx))]=(x)/(2), x in (0,(pi)/(4)).`

Answer» `L.H.S."=[(sqrt(1+sinx)+sqrt(1-sinx))/(sqrt(1+sinx)-sqrt(1-sinx))]`
`=cot^(-1)[(sqrt(cos^(2).(x)/(2)+sin^(2).(x)/(2)+2sin.(x)/(2)cos.(x)/(2))+sqrt(cos^(2).(x)/(2)+sin^(2).(x)/(2)-2sin.(x)/(2)cos.(x)/(2)))/(sqrt(cos^(2).(x)/(2)+sin^(2).(x)/(2)+2sin.(x)/(2)cos.(x)/(2))-sqrt(cos^(2).(x)/(2)+sin^(2).(x)/(2)-2sin.(x)/(2)cos.(x)/(2)))],`
`[because cos^(2).(x)/(2)+sin^(2).(x)/(2)-1" और "sinx=2sin.(x)/(2)cos.(x)/(2)]`
`=cot^(-1)[(sqrt((cos.(x)/(2)+sin.(x)/(2))^(2))+sqrt((cos.(x)/(2)-sin.(x)/(2))))/(sqrt((cos.(x)/(2)+sin.(x)/(2))^(2))-sqrt((cos.(x)/(2)-sin.(x)/(2))^(2)))]`
`=cot^(-1)[((cos.(x)/(2)+sin.(x)/(2))+(cos.(x)/(2)-sin.(x)/(2)))/((cos.(x)/(2)-sin.(x)/(2))-(cos.(x)/(2)-sin.(x)/(2)))],`
`[because 0lt (x)/(2)lt(pi)/(4)" और "cos.(x)/(2) gt 0, sin.(x)/(2) gt 0]`
`=cot^(-1)[(2cos.(x)/(2))/(2sin.(x)/(2))]`
`=cot^(-1)(cot.(x)/(2))`
`=(x)/(2)`
= R.H.S.`" "`यही सिद्ध करना था।
257.

सिद्ध कीजिए कि - `(9pi)/(8)-(9)/(4)sin^(-1)((1)/(3))=(9)/(4)sin^(-1)((2sqrt2)/(3)).`

Answer» `L.H.S.=(9pi)/(8)-(9)/(4)sin^(-1)((1)/(3))`
`=(9)/(4)[(pi)/(2)-sin^(-1)((1)/(3))]`
`=(9)/(4)[cos^(-1)((1)/(3))]," "[because sin^(-1)x+cos^(-1)x=(pi)/(2)]`
`=(9)/(4)sin^(-1)(sqrt(1-(1)/(9)))," "[because cos^(-1)x=sin^(-1)sqrt(1-x^(2))]`
`=(9)/(4)sin^(-1)(sqrt((8)/(9)))`
`=(9)/(4)sin^(-1)((2sqrt2)/(3))`
= R.H.S.`" "` यही सिद्ध करना था ।
258.

मान ज्ञात कीजिए - `"cosec"^(-1)(-1)`

Answer» Correct Answer - `-(pi)/(2)`
259.

यदि `tan^(-1)""(3)/(4)=x" तो "secx` का मान ज्ञात कीजिए।

Answer» Correct Answer - `(5)/(4)`
260.

`tan[(1)/(2)cos^(-1)""(sqrt(5))/(3)]` का मान ज्ञात कीजिए ।

Answer» Correct Answer - `(3-sqrt(5))/(2)`
261.

निम्नलिखित समीकरण को हल कीजिए - `tan^(-1)((1-x)/(1+x))=(1)/(2)tan^(-1)x, (x gt0).`

Answer» यहाँ `tan^(-1)((1-x)/(1+x))=(1)/(2)tan^(-1)x`
`x=tan theta` रखने पर
`tan^(-1)[(1-tan theta)/(1+tan theta)]=(1)/(2)tan^(-1)(tan theta)`
`rArr tan^(-1)[(tan.(pi)/(4)-tan theta)/(1+tan.(pi)/(4)tan theta)]=(1)/(2)theta`
`rArr tan^(-1)[tan((pi)/(4)-theta)]=(1)/(2)theta,`
`" "[because tan(A-B)=(tan A-tanB)/(1+tanA tanB)]`
`rArr" "(pi)/(4)-theta=(1)/(2)theta`
`rArr" "(3)/(2)theta=(pi)/(4)`
`rArr" "theta=(pi)/(6)`
`rArr" "tan^(-1)x=((pi)/(6))`
`rArr" "x=(1)/(3).`
262.

सिद्ध कीजिए - `tan^(-1)((sqrt(1+x)-sqrt(1-x))/(sqrt(1+x)+sqrt(1-x)))=(pi)/(4)-(1)/(2)cos^(-1)x, -(1)/(sqrt2)le x le1.`

Answer» `L.H.S.=tan^(-1)((sqrt(1+x)-sqrt(1-x))/(sqrt(1+x)+sqrt(1-x)))`
`x=cos2theta` रखने पर,
`=tan^(-1)[(sqrt(1+cos2theta)-sqrt(1-cos 2theta))/(sqrt(1+cos 2theta)+sqrt(1-cos 2theta))]`
`=tan^(-1)[(sqrt(1+(2cos^(2)theta-1))-sqrt(1-(1-2sin^(2)theta)))/(sqrt(1+(2cos^(2)theta-1))+sqrt(1-(1-2sin^(2)theta)))],`
`" "[because cos 2theta=2cos^(2)theta-1=1-2sin^(2)theta]`
`=tan^(-1)[(sqrt(2cos^(2)theta)-sqrt(2sin^(2)theta))/(sqrt(2cos^(2)theta)+sqrt(2sin^(2)theta))]`
`=tan^(-1)[(sqrt2cos theta-sqrt2sin theta)/(sqrt2cos theta+sqrt2sin theta)]`
`=tan^(-1)[(cos theta=sin theta)/(cos theta+sin theta)]`
`=tan^(-1)[(1-tan theta)/(1+tan theta)],`
[अंश और हर को `cos theta` से भाग देने पर ]
`=tan^(-1)[(tan.(pi)/(4)-tantheta)/(1+tan.(pi)/(4).tan theta)],`
`" "[because tan (A-B)=(tanA-tanB)/(1+tan Atan B)]`
`=tan^(-1)[tan((pi)/(4)-theta)]`
`=(pi)/(4)-theta`
`=(pi)/(4)-(1)/(2)cos^(-1)x`
`[because x=cos 2theta rArr 2 theta cos^(-1)x rArr theta=(1)/(2)cos^(-1)x]" "=(x)/(2)`
= R.H.S. यही सिद्ध करना था ।
263.

मान ज्ञात कीजिए - `cos^(-1)""(-(1)/(sqrt(2)))`

Answer» Correct Answer - `(3pi)/(4)`
264.

`tan^(-1)""((sqrt(1+x^(2))-1)/(x))` का मान `tan^(-1) ` के पदों में ज्ञात कीजिए ।

Answer» Correct Answer - `(1)/(2) tan^(-1)x`
265.

मूल्यांकन कीजिए `sin[2cos^(-1)(-(3)/(5))]`

Answer» माना `cos^(-1)(-(3)/(5))=theta`, जहाँ `theta=[0, pi]`
तब `" "cos theta=-(3)/(5)`
चूँकि `" "theta in [0,pi],` तब `sin theta gt 0`
`therefore" "sin theta =sqrt(1-cos^(2)theta)`
`=sqrt(1-(-(3)/(5))^(2))=sqrt(1-(9)/(25))`
`=sqrt((25-9)/(25))=sqrt((16)/(25))=(4)/(5)`
266.

यदि `cos^(-1)x=(pi)/(3)" तो "sin^(-1)x` का मान ज्ञात कीजिए।

Answer» Correct Answer - `(pi)/(6)`
267.

सिद्ध कीजिए - `tan^(-1)sqrtx=(1)/(2)cos^(-1)((1-x)/(1+x)),x in (0,1)`.

Answer» माना `" "tan^(-1)sqrtx=theta, theta in (-(pi)/(2),(pi)/(2))`
तब `" "sqrtx=tan theta`
`rArr" "x=tan^(2)theta`
हम जानते हैं कि,
`cos2 theta=(1-tan^(2)theta)/(1+tan^(2)theta)`
`rArr" "cos 2 theta=(1-x)/(1+x)`
`rArr" "2theta=cos^(-1)((1-x)/(1+x))`
`rArr" "theta=(1)/(2)cos^(-1)((1-x)/(1+x))`
`rArr" "tan^(-1)sqrtx=(1)/(2)cos^(-1)((1-x)/(1+x))`
यही सिद्ध करना था।
268.

मान ज्ञात कीजिए - ` sec^(-1)(-sqrt(2))`

Answer» Correct Answer - `(3pi)/(4)`
`sec^(-1)(-sqrt(2))=x`
`implies sec x =-sqrt(2)=-sec""(pi)/(4)=sec(pi-(pi)/(4))=sec""(3pi)/(4)`
`implies x=(3pi)/(4)`
269.

निम्नलिखित के मुख्य मान ज्ञात कीजिए : `sin^(-1)((1)/(sqrt2))`

Answer» Correct Answer - (i) `(pi)/(4)` (ii) `(pi)/(6)` (iii) `(pi)/(3)` (iv) `(pi)/(4)` (v) 0 (vi) `(pi)/(4)`
270.

मूल्यांकन कीजिए `sin{(pi)/(3)-sin^(-1)(-(1)/(2))}`

Answer» माना `sin[(pi)/(3)-sin^(-1)(-(1)/(2))]`
`=sin[(pi)/(3)-{-sin^(-1).(1)/(2)}].`
`" "[because sin^(-1)(-x)=-sin^(-1)x]`
`=sin[(pi)/(3)+sin^(-1)(sin.(pi)/(6))]`
`" "[because (pi)/(6) in [-(pi)/(2),(pi)/(2)]]`
`=sin[(pi)/(3)+(pi)/(6)]`
`=sin.(pi)/(2)=1.`
271.

यदि `tan^(-1)""(x-1)/(x-2)+tan^(-1)""(x+1)/(x+2)=(pi)/(4)`, तो x का मान ज्ञात कीजिए।

Answer» `tan^(-1)""(x-1)/(x-2)+tan^(-1)""(x+1)/(x+2)=(pi)/(4)`
`impliestan^(-1)""((x-1)/(x-2)+(x+1)/(x+2))/(1-(x-1)/(x-2).(x+1)/(x+2))=tan^(-1)1`
`implies((x-1)+(x+2)+(x+1)(x-2))/((x-2)(x+2)-(x-1)(x+1))=1`
`implies(x^(2)+x-2+x^(2)-x-2)/((x^(2)-4)-(x^(2)-1))=1`
`implies(2x^(2)-4)/(-3)=1implies2x^(2)-4=-3`
`implies2x^(2)=1impliesx^(2)=(1)/(2)impliesx=+-(1)/(sqrt2)`
272.

`tan^(-1)sqrtx=(1)/(2)cos^(-1)((1-x)/(1+x)),x""in[0,1]`

Answer» माना `sqrt3=tanthetaimpliesx=tan^(2)theta`
`R.H.S.=(1)/(2)cos^(-1)((1-x)/(1+x))" "x"in[0,1]`
`=(1)/(2)cos^(-1)((1-tan^(2)theta)/(1+tan^(2)theta))`
`=(1)/(2)cos^(-1)(cos2theta)=(1)/(2)(2theta)`
`=theta=tan^(-1)sqrt(x)=L.H.S.`
273.

निम्नलिखित के मुख्य मान ज्ञात कीजिए : `sin^(-1)((-sqrt3)/(2))`

Answer» Correct Answer - (i) `-(pi)/(4)` (ii) `(5pi)/(6)` (iii) `(2pi)/(3)` (iv) `(5pi)/(6)` (v) `-(pi)/(4)` (vi) `-(pi)/(2)`.
274.

मूल्यांकन कीजिए `sin(cot^(-1)x)`

Answer» माना `cot^(-1)x=theta`, जहाँ `theta in (0,pi)`
तब `cot theta=x`
चूँकि `theta in (0,pi)` इसलिए `sin theta gt 0`
`therefore" "sin theta=(1)/("cosec" theta)=(1)/(sqrt(1+cot^(2)theta))`
`=(1)/(sqrt(1+x^(2)))`
`rArr" "sin(cot^(-1)x)=(1)/(sqrt(1+x^(2)))`
275.

`tan(sin^(-1)""(3)/(5)+cot^(-1)""(3)/(2))`

Answer» `tan(sin^(-1)""(3)/(5)+cot^(-1)""(3)/(2))`
`=tan[tan^(-1)""((3)/(5))/(sqrt(1-((3)/(5))^(2)))+tan^(-1)""(2)/(3)]`
`=tan[tan^(-1)""(3)/(4)+tan^(-1)""(2)/(3)]`
`tan[tan^(-1)""((3)/(4)+(2)/(3))/(1-(3)/(4).(2)/(3))]=((9+8)/(12))/((12-6)/12)=(17)/(6)`
276.

`tan^(-1)""(1)/(5)+tan^(-1)""(1)/(7)+tan^(-1)""(1)/(3)+tan^(-1)""(1)/(8)=(pi)/(4)`

Answer» `L.H.S.=tan^(-1)""(1)/(5)+tan^(-1)""(1)/(7)+tan^(-1)""(1)/(3)+tan^(-1)""(1)/(8)`
`=tan^(-1)""((1)/(5)+(1)/(7))/(1-(1)/(5)xx(1)/(7))+tan^(-1)""((1)/(3)+(1)/(8))/(1-(1)/(3)xx(1)/(8))`
`=tan^(-1)""((7+5)/(35))/((35-1)/(35))+tan^(-1)""((8+3)/(24))/((24-1)/(24))`
`=tan^(-1)""(6)/(17)+tan^(-1)""(11)/(23)`
`=tan^(-1)""((6)/(17)+(11)/(23))/(1-(6)/(17)xx(11)/23)=tan^(-1)""((138+187)/(391))/((391-66)/(391))`
`=tan^(-1)""(325)/(325)=tan^(-1)1=(pi)/(4)=R.H.S.`
277.

निम्नलिखित के मुख्य मान ज्ञात कीजिए। (i) `sin^(-1)""(1)/(2)` (ii) `tan^(-1)""(1)/(sqrt3)` (iii) `cot^(-1)(-sqrt3)`

Answer» (i) `sin^(-1)""(1)/(2)=sin^(-1)""(sin""(pi)/(6))=(pi)/(6)`
(ii) `tan^(-1)""(1)/(sqrt3)=tan^(-1)(tan""(pi)/(6))=(pi)/(6)`
(iii) `cot^(-1)(sqrt-3)=pi-cot^(-1)(sqrt3)=pi-cot^(-1)(cot""(pi)/(6))=pi-(pi)/(6)=(5pi)/(6)`
278.

निम्नलिखित का मान ज्ञात कीजिए - `sec(sec^(-1).(27)/(10)).`

Answer» `sec(sec^(-1).(27)/(10))=(27)/(10)," "[because(27)/(10) gt 1]`
279.

`cos^(-1)""(4)/(5)+cos^(-1)""(12)/(13)=cos^(-1)""(33)/(65)`

Answer» `L.H.S.cos^(-1)""(4)/(5)+cos^(-1)""(12)/(13)`
`=cos^(-1)[(4)/(5)xx(12)/(13)-sqrt(1-((4)/(5))^(2))sqrt(1-((12)/(13))^(2))]`
`=cos^(-1)[(48)/(65)-(3)/(5)xx(5)/(13)]=cos^(-1)((48)/(65)-(15)/(65))`
`=cos^(-1)""(33)/(65)=R.H.S.`
280.

निम्नलिखित व्यंजकों के मान ज्ञात कीजिए - `cos^(-1)(cos.(2pi)/(4))`

Answer» `cos^(-1)(cos.(2pi)/(4))=(2pi)/(4)," "[because (2pi)/(4) in [0, pi]]`
281.

`sin((pi)/(3)-sin^(-1)(-(1)/(2)))` का मान है :A. `(1)/(2)`B. `(1)/(3)`C. `(1)/(4)`D. 1

Answer» Correct Answer - D
`sin[(pi)/(3)-sin^(-1)(-(1)/(2))]`
`=sin[(pi)/(3)+sin^(-1)""(1)/(2)]`
`=sin[(pi)/(3)+sin^(-1)(sin""(pi)/(6))]`
`=sin[(pi)/(3)+(pi)/(6)]`
`=sin""(pi)/(2)=1`
282.

निम्नलिखित का मान ज्ञात कीजिए - `sin(sin^(-1)((-1)/(2)))`

Answer» `sin(sin^(-1)(-(1)/(2)))=-(1)/(2)," "[because-(1)/(2) in [-1,1]]`
283.

`tan^(-1)sqrt3-cot^(-1)(-sqrt3)` का मान है :A. `pi`B. `-(pi)/(2)`C. 0D. `2sqrt3`

Answer» Correct Answer - B
`tan^(-1)sqrt3-cot^(-1)(-sqrt3)`
`=tan^(-1)sqrt3-(pi-cot^(-1)sqrt3)`
`=tan^(-1)sqrt3-pi+cot^(-1)sqrt3`
`=(tan^(-1)sqrt3+cot^(-1)sqrt3)-pi`
`=(pi)/(2)-pi=-(pi)/(2)`
284.

`tan^(-1)(tan""(7pi)/(6))`

Answer» `tan^(-1)(tan""(7pi)/(6))=tan^(-1)[tan(pi+(pi)/(6))]`
`=tan^(-1)(tan""(pi)/(6))=(pi)/(6)`
285.

निम्नलिखित व्यंजकों के मान ज्ञात कीजिए - `cos^(-1)(cos.(2pi)/(3))+sin^(-1)(sin.(2pi)/(3))`

Answer» चूँकि `cos^(-1)` की मुख्य शाखा का परिसर `[0,pi]` और `sin^(-1)` का `[-(pi)/(2),(pi)/(2)]` होता है।
`therefore" "cos^(-1)(cos.(2pi)/(3))+sin^(-1)(sin.(2pi)/(3))`
`=(2pi)/(3)+sin^(-1)[sin(pi-(pi)/(3))]`
`=(2pi)/(3)+sin^(-1)(sin.(pi)/(3))," "[because sin(pi-theta)=sin theta]`
`=(2pi)/(3)+(pi)/(3)=(3pi)/(3)=pi.`
286.

निम्नलिखित व्यंजकों के मान ज्ञात कीजिए - `tan^(-1)(tan.(3pi)/(4))`

Answer» चूँकि `tan^(-1)` की मुख्य शाखा का परिसर `(-(pi)/(2),(pi)/(2))` होता है।
`therefore" "tan^(-1)(tan.(3pi)/(4))ne(3pi)/(4)," "[because (3pi)/(4) cancel in (-(pi)/(2),(pi)/(2))]`
अब , `tan^(-1)(tan.(3pi)/(4))`
`=tan^(-1)[tanpi-((pi)/(4))]," "[because (3pi)/(4)=pi-(pi)/(4)]`
`=tan^(-1)[-tan((pi)/(4))],`
`" "[because tan(pi-theta)=-tan theta]`
`=tan^(-1)[tan(-(pi)/(4))]," "[because tan(-theta)=-tan theta]`
`=-(pi)/(4) in (-(pi)/(2),(pi)/(2))," "[because tan^(-1)(tan theta)=theta]`
`therefore" "tan^(-1)(tan.(3pi)/(4))=-(pi)/(4).`
287.

निम्नलिखित व्यंजकों के मान ज्ञात कीजिए - `cos^(-1)(cos.(13pi)/(6))`

Answer» चूँकि `cos^(-1)` की मुख्य शाखा का परिसर `[0,pi]` होता है।
`therefore" "cos^(-1)(cos.(13pi)/(6))ne(13pi)/(6)," "[because(13pi)/(6) cancel in [0,pi]]`
अब, `cos^(-1)(cos.(13pi)/(6))`
`=cos^(-1)[cos(2pi+(pi)/(6))]," "[because(13pi)/(6)=2pi+(pi)/(6)]`
`=cos^(-1)(cos.(pi)/(6))," "[because cos(2pi+theta)=cos theta]`
`=(pi)/(6)in [0,pi]," "[because cos^(-1)(cos theta)=theta]`
`therefore cos^(-1)(cos.(13pi)/(6))=(pi)/(6).`
288.

मान निकालें : `cos^(-1)cos((13pi)/(6))`

Answer» Correct Answer - `(pi)/(6)`
289.

`cos^(-1)(cos""(13pi)/(6))`

Answer» `cos^(-1)(cos""(13pi)/(6))=cos^(-1)[cos(2pi+(pi)/(6))]`
`=cos^(-1)(cos""(pi)/(6))=(pi)/(6)`
290.

`cos^(-1)(cos""(13pi)/(6))` का मान ज्ञात कीजिए ।

Answer» Correct Answer - `(pi)/(6)`
291.

सिद्ध कीजिए कि `tan^(-1)""(1)/(4)+tan^(-1)""(2)/(9)=(1)/(2)cos^(-1)""(3)/(5)`

Answer» बायाँ पक्ष `=tan^(-1)""(1)/(4)+tan^(-1)""(2)/(9)`
`= tan^(-1)(((1)/(4)+(2)/(9))/(1-(1)/(4) xx (2)/(9)))=tan^(-1)""((17)/(34))=tan^(-1)""(1)/(2)`
दायें पक्ष में , माना
` (1)/(2) cos^(-1)""(3)/(5)=thetaimplies cos2 theta=(3)/(5)`
`:. tan theta=sqrt((1-cos2theta)/(1+cos 2 theta))=sqrt((1-3//5)/(1+3//5))`
`tan theta=(1)/(2)implies theta=tan^(-1)""(1)/(2)`
`implies` बायाँ पक्ष = दायाँ पक्ष
292.

सिद्ध कीजिए कि `cos^(-1)""((63)/(65))+2 tan^(-1)""(1)/(5))=sin^(-1)""(3)/(5)`

Answer» हम जानते है कि
` 2tan^(-1)x=cos^(-1)((1-x^(2))/(1+x^(2)))`
` 2 tan^(-1)""(1)/(5)=cos^(-1)((1-1//25)/(1+1//25))`
`= cos^(-1)((24)/(26))=cos^(-1)((12)/(13))`
`:.` दिये गये समीकरण से
` cos^(-1)""((63)/(65))+cos^(-1)((12)/(13))`
`=cos^(-1)[(63)/(65) xx (12)/(13)-sqrt(1-((63)/(65))^(2))sqrt(1-((12)/(13))^(2))]`
`= cos^(-1)[(756)/(845)-(80)/(845)]`
` =cos^(-1)[(676)/(845)]=sin^(-1)sqrt(1-((676)/(845))^(2))`
`=sin^(-1)((507)/(845))`
`implies cos^(-1)""(63)/(65)+cos^(-1)""(12)/(13)=sin^(-1)""(3)/(5)`