Question

If A + B = 90° and cos B = 3/5, what is the value of sin A?

Answer 1

Step-by-step explanation:

A+B=90

⇒B=90-A

cos B=3/5

⇒cos (90-A)=3/5 [∵B=90-A]

⇒sin A=3/5 [∵cos(90-A)=sin A].

Answer 2

Given : cos B = 3/5 , A + B = 90°  

To find : The value of sin A

Solution :  

A + B = 90°  

A = 90° - B  

On putting sin on both sides,   we obtain ,

sin A = sin(90° - B )

sin A = cos B

[ sin (90° -θ ) = cos θ )]

sin A = 3/5

[cos B = 3/5]

Hence, the value of sin A  is 3/5 .

 

Extra information  :  

• Trigonometry is the study of the relationship between the sides and angles of a triangle.
• Two angles are said to be complementary if their sum is equal to 90° .
• θ & (90° - θ) are complementary angles.

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