y=1.2x2+2x+9
First, transfer 9 to the other side of the equation.
y−9=1.2x2+2x
Factor out the coefficient of x2.
y−9=1.2(x2+2x1.2)
y−9=1.2(x2+53x)
Now, we will compute for the value that we can add to x2+53x to make it a perfect square. Divide the coefficient of x by 2 and multiply it by itself.
53÷2=56
(56)(56)=2536
Add 2536 inside the parentheses. We must also add 1.2(2536) to the other side to maintain equality.
y−9+1.2(2536)=1.2(x2+53x+2536)
y−9+56=1.2(x2+53x+2536)
y−496=1.2(x2+53x+2536)
Factor out x2+53x+2536. We made this into a perfect square trinomial so it should be easy.
y−496=1.2(x+56)(x+56)
y−496=1.2(x+56)2
Transfer 496 to the other side of the equation then you're done.
y=1.2(x+56)2+496
