Question

if cos(90°-A)=0 then sin (a+b)=


A)0
B)2
C)3
D)non of these​

Answer 1

Given : Cos (90° - A)  = 0

To Find :  Sin (A + B)

Solution:

Method 1 :

Cos (90° - A)  = 0

=> Sin A = 0

=> A = nπ

Sin (A + B) = Sin ( nπ + B)  = ± SinB

Method 2 :

Cos (90° - A)  = 0

=> Sin A = 0

Sin²A + Cos²A = 1

=> Cos²A  = 1

=> Cos A = ±1

Sin (A + B) = SinACosB + CosASinB

=> Sin (A + B) =  0 *CosB +  ( ±1)SinB

=> Sin (A + B) =     0   ±  SinB

=> Sin (A + B) =    ±  SinB

Sin (A + B) =    ±  SinB

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