3x^2 = 2x^2 + 25
(Taking 2x^2 to the LHS)
3x^2 - 2x^2 = 25
1x^2 = 25
(Taking square roots on both sides)
x = root25
x = +5 or -5
(as both answers lead to 25
-5 * -5 = +25
+5 * +5 = +25)
You may write the answer as +5 according to your convenience.
Hope this helped!
