How can I solve 2x^{2}-3=15
Isolate the x term onto one side of the equation, divide both sides by the constant of the x term, and take the square root of both sides.
2x^{2} - 3 = 15
2x^{2 }= 18
x^{2} = 9
x = 3 or x = -3
Note that the square root of 9 is 3 or -3, both are solutions.
(-3)^{2} = -3*-3= 9