# What is cos(3.14-angle)?

### 1 Answer | Add Yours

You should come up with the substitution `alpha = angle ` and `3.14 = pi` .

You need to expand the cosine using the formula `cos(x-y) = cosx*cosy + sin x*sin y` such that:

`cos(pi - alpha) = cos pi*cos alpha + sin pi*sin alpha`

Using `cos pi = -1` and `sin pi = 0` yields:

`cos(pi - alpha) = -cos alpha + 0*sin alpha`

`cos(pi - alpha) = -cos alpha`

**Hence, evaluating `cos(pi - alpha)` yields the negative value of cos alpha such that: `cos(pi - alpha) = -cos alpha` .**