Question

the value of cos(90 - x) cos(90 - y)-sin(90 - x)sin(90 - y)​

Answer 1

Answer:

-cos (x+y)​

Step-by-step explanation:

cos(90-x) = sin x

cos(90-y) = sin y

sin(90-x) = cos x

sin(90-y) = cos y

cos(90 - x) cos(90 - y)-sin(90 - x)sin(90 - y)​

= ( sin x * sin y ) - (cos x * cos y)

= sin x sin y -cos x cos y

= -(cos x cos y - sin x sin y )

= - cos(x+y)