Presuming you mean y = -2x^2 - 8x - 13
Firstly, put the x terms in parentheses and factor out -2:
[tex] y=-2(x^2+4x)-13 [/tex]
Next, we want to make what's inside those parentheses a perfect square. To do this, divide the x coefficient by 2 and square that result. In this case, that result is 4. Add 4 to the inside of the parentheses, and add 8 to the outside of the parentheses to balance it out. (Since when foiled, 4 x -2 = -8)
[tex] y=-2(x^2+4x+4)-13+8\\y=-2(x^2+4x+4)-5 [/tex]
Next, factor what's inside the parentheses, and your final answer will be [tex] y=-2(x+2)^2-5 [/tex]
