1.

In `Delta ABC`, right angled at A, `cos^(-1)((R )/(r_(2)+r_(3)))` isA. `30^(@)`B. `60^(@)`C. `90^(@)`D. `45^(@)`

Answer» Correct Answer - B
`r_(2)+r_(3)=4R"cos"^(2)(A)/(2)`
`angle A=90^(@)`
`therefore cos^(-1)((R )/(r_(2)+r_(3)))`
`=cos^(-1)((R )/(4"R cos"^(2)(A)/(2)))`
`="cos"^(-1)(1)/(2)`
`=60^(@)`


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