Quadratic

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 .....