Question

Which relationship in the triangle must be true ?

Answer 1

Choice B. sin(B)=cos(90-B)

Explanation:

That cofunction identity is the one you looking for...choice B.

If you aren't convinced or don't know that identity, then maybe this will help:

90-B is actually the same thing as saying A for this right triangle since A+B=90.

So choice B basically says sin(B)=cos(A)

Well let's find both sin(B) and cos(A)

sin(B)=b/c

cos(A)=b/c

Those are the same ratios!

So they are equal!

Answer 2

option B

Explanation:

from the given options

a) sin (B) = sin (A)

b) sin (B ) = cos (90° - B)

cos (90° - B ) = Sin B

c) cos (B ) = sin(180° - B)

sin(180° - B) = sin (B)

d) cos (B) = cos(A)

so, we can clearly see from the above solution that option B is correct.

As 90° - B is in first quadrant and in first quadrant sign of cos dose not change and 90 is multiple of odd so 'cos' changes to 'sin'