Question

factor completely.
$72z^2 - 50$

Explanation:

Step1: Factor out GCF

$72z^2 - 50 = 2(36z^2 - 25)$

Step2: Apply difference of squares

Recall $a^2 - b^2=(a-b)(a+b)$. Here $36z^2=(6z)^2$, $25=5^2$.
$2(36z^2 - 25)=2(6z-5)(6z+5)$

Answer:

$2(6z - 5)(6z + 5)$