You need to 'complete the square for x '
2x^2 + 6x + 11
2 (x^2 + 3x) + 11 take 1/2 of the 'x' coefficient : 1.5
2 ( x+1.5)2 + 11 if you expand this out , you will find that you have added 2 * 1.52 to the expression....
so you need to subtract that amount to keep the original equation
2(x+1.5)^2 - 2 * 1.52 +11
2 ( x+1.5)2 + 6.5 is the final form..... take it from here .....