Question

Solve the equation by Factoring

Answer 1

First set the equation to zero by adding -400 to both sides.
$16 {r}^{2} - 400 = 0$
Next factor 16
$16 ({r}^{2} - 25)= 0$

Divide through by 16
$\frac{16 ({r}^{2} - 25)}{16} = \frac{0}{16}$
$({r}^{2} - 25)= 0$

This is difference of two squares

$(r - 5)(r + 5) = 0$
$either \: r - 5= 0 \: or \: r + 5= 0$
$r = 5 \: or \: - 5$