Question

In `triangle PQR`, how do you express cosQ in terms of p, q, r?

Answer 1

`cosQ=(p^2+r^2-q^2)/(2pr)`

Explanation:

Here side `p` is opposite `/_P`, side `q` is opposite `/_Q` and side `r` is opposite `/_R`.

`cosQ` is then (sum of squares of other (other than `q`) two sides minus square of side opposite `/_Q` i.e `q`) divided by (twice the product of other two sides).