if f(x)=cos(5x) find f(ð/4)

To find f(π/4), you need to substitute π/4 into the function f(x) = cos(5x) and evaluate it.

The cosine function evaluates the cosine of an angle. In this case, the angle is 5x. So, you need to substitute π/4 into the expression for x.

f(π/4) = cos(5(π/4))

Now, let's simplify this expression step by step:

1. Multiply 5 by π/4:
f(π/4) = cos(5π/4)

2. Simplify 5π/4:
f(π/4) = cos(π/4)

The cosine of π/4 is a commonly known value. It is equal to √2/2.

f(π/4) = √2/2

Therefore, f(π/4) is equal to √2/2.