Question

Sin81sin36+cos81cos36

Answer 1

cos(81-36) =cos81cos36+sin81+sin36

Answer 2

To simplify the trigonometric expression "sin(81)sin(36) + cos(81)cos(36)", we can use the identity:

cos(A - B) = cos(A)cos(B) + sin(A)sin(B)

So, in this case, we can rewrite the expression as:

cos(81 - 36)

Now, let's calculate the value:

cos(81 - 36) = cos(45)

The angle 45 degrees is well-known and can be easily evaluated:

cos(45°) = sqrt(2)/2 ≈ 0.7071

So, the simplified value of the expression is approximately 0.7071.