### Home > PC3 > Chapter Ch8 > Lesson 8.2.2 > Problem8-74

8-74.

Given $s^{2} + c^{2} = 1$, rewrite the following expressions using only $c$.

1. $c^{2} – s^{2}$

Rewrite the given equation for $s^{2}$.
Then substitute in that expression.

1. $\frac { c } { 1 + s } + \frac { c } { 1 - s }$

$\frac{c}{1+s}\cdot\frac{1-s}{1-s}+\frac{c}{1-s}\cdot\frac{1+s}{1+s}$