1.

यदि `sin(A-B)=(1)/(2)` और `cos(A+B)` जहाँ और न्यूनकोण है तो `B` का मान ज्ञात करे?A. `(pi)/(6)`B. `(pi)/(12)`C. `(pi)/(4)`D. `(pi)/(2)`

Answer» Correct Answer - b
`sin(A-B)=(1)/(2)(A-B=30^(@))`
`cos(A+B)=(1)/(2)(A+B= 60^(@))`
Adding both side
`rArr(A-B)(A+B)=30^(@)+ 60^(@)`
`rArr2A=90^(@)`
`rArrA=45^(@)`
`because A-B=20^(@)`
`B=A-30^(@)=45^(@).30^(@)=15^(@)`
`rArr(15xxpi)/(180)=(pi)/(12)` radian.


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