# How do you factor completely 4x^2-25?

$\left(2 x + 5\right) \left(2 x - 5\right)$
Realize that $4 {x}^{2} - 25$ is a difference of squares. Differences of squares, such as ${a}^{2} - {b}^{2}$, can be factored into $\left(a + b\right) \left(a - b\right)$.
Since $4 {x}^{2} = {\left(2 x\right)}^{2}$ and $25 = {\left(5\right)}^{2}$, we can say that 4x^2-25=color(blue)((2x+5)(2x-5).