How do you convert p(x) = -8x^2 - 64x to vertex form?

I know the answer is p(x) = -8(x + 4)^2 + 128, but I'm unaware of the steps taken to get to that stage.

Any help is appreciated, thanks!

Step-by-step explanation:

Given,

Take -8 factor common,

which can be written as

Add and subtract by 16 inside bracket,

step-by-step explanation:

y = | -2(-2) |     →     y = | 4 |     →     y = 4       ⇒   (-2, 4)

y = | -2(-1) |     →     y = | 2 |     →       y =   2       ⇒   (-1, 2)    

y = | -2(0) |     →     y = | 0 |     →       y = 0         ⇒   (0, 0)

y = | -2(1) |   c →     y = | -2 |     →     y =   2         ⇒   (1, 2)    

y = | -2(2) |     →     y = | - 4 |     →     y =   4         ⇒   (2, 4)