find adddition of cos and sin

Question

cos a=1/3 ans sinb =1/y when a is between 0 and 70 and b is between 90 and 180 find cos (a+B)

Answer 1

This can be worked using a trig identity of cos (A + B) = (cos A)(cos B) -(sin A)(sin B)

Let us list the values:

cos A = 1/3 and was given

cos B = - (y^2-1)^1/2 / (y), a minus because the sine is negative in the second quadrant

Sin A = (8)^1/2

Sin B = 1/y and was given.

The non given values were calculated by using the pythagoean theorem

So, plug thee into the identity and evaluate it and you are done.

Answer 2

a=70.53 The best I can do.

1/y? I can use any amount between 90 and 180 then adjust it so 1 is the numerator.

cos30+sin30=1.366?