X^2+2x^2=18

To solve the equation x^2 + 2x^2 = 18, we can combine like terms on the left side of the equation:

3x^2 = 18

Next, we can divide both sides of the equation by 3 to isolate x^2:

x^2 = 6

To find the value(s) of x, we can take the square root of both sides of the equation:

x = ±√6

So the solutions to the equation x^2 + 2x^2 = 18 are x = √6 and x = -√6.