Answer
The solution set is $\left\{-5, 5\right\}$.
Work Step by Step
Divide 3 to both sides to obtain:
$x^2 = 25$
Add $-25$ to both sides to obtain:
$x^2-25 = 0
\\x^2-5^2=0$
RECALL:
A difference of two squares can be factored using the formula:
$a^2-b^2=(a-b)(a+b)$
Factor the difference of two squares to obtain:
$(x-5)(x+5)=0$
Equate each factor to 0, and then solve each equation to have:
$x-5=0 \text{ or } x+5 = 0
x=5 \text{ or } x=-5$
The solution set is $\left\{-5, 5\right\}$.
