Split: How to sketch this parabola problem..

[candy101]

thts so cool (i actually manage to get something right..of course with a few errors)


i got this other problem which i am trying to figure out

how would i complete the square for this y=3x^2+12x-15
(its a parabola question)

my teacher got this===> y=3(x^2+4x+4) -15-12

which equals==> y= 3(x+2)^2 + -27
and the vertex is (-2,-27)

i mean i know how to complete the square but i have no idea what he did here.... can some one please explain ==>

if he divided 12x by 3 shouldn't the 3's cancel out?? and y would he then move the 12 over even though it had already been divided by 3?

thanks,

 

[Deleted member 4993]

thts so cool (i actually manage to get something right..of course with a few errors)


i got this other problem which i am trying to figure out

how would i complete the square for this y=3x^2+12x-15
(its a parabola question)

3x[sup:17r1hs5q]2[/sup:17r1hs5q] + 12 x - 15

= 3(x[sup:17r1hs5q]2[/sup:17r1hs5q] + 4x) - 15

= 3(x[sup:17r1hs5q]2[/sup:17r1hs5q] + 2 * 2 * x + 2[sup:17r1hs5q]2[/sup:17r1hs5q]) - 3 * 2[sup:17r1hs5q]2[/sup:17r1hs5q]- 15

= 3(x - 2)[sup:17r1hs5q]2[/sup:17r1hs5q] - 12 - 15


my teacher got this===> y=3(x^2+4x+4) -15-12

which equals==> y= 3(x+2)^2 + -27
and the vertex is (-2,-27)

i mean i know how to complete the square but i have no idea what he did here.... can some one please explain ==>

if he divided 12x by 3 shouldn't the 3's cancel out?? and y would he then move the 12 over even though it had already been divided by 3?

thanks,

Is that any better?

Please start a new thread with a new problem