Which relationship in the triangle must be true? sin (b) = sin (a) sin (b) = cos (90 -

b. cos (b) = sin (180 -

b. cos (b) = cos (a) ?

Assuming angle a and angle b are not equal and the given triangle is a right triangle.

Let's see cos (90-b)

Here we use the formula of cos (A-B) = cos A cos B - sin A sin B

And on using this formula, we will get

cos (90-b) = cos 90 cos b + sin 90 sin b

Value of cos 90 = 0 and sin 90 = 1, And on using these values, we will get

cos (90-b) = (0) cos (b) + (1) sin (b)

cos (90-b) = 0 + sin (b)

cos (90-b) = sin (b)

As we see that on using the formula, we are getting cos (90-b) = sin b.

So the correct option is cos (90-b) = sin b