Question

(picture) where did the 9 come from?

Answer 1

the 9 is there to complete the square

Answer 2

sorry i don't exactly know what that means? In the parenthesis?

Answer 3

completing the square method

you had x^2 + 6x <---for this to become a perfect square trinomial you need to add 9 because x^2 + 6x + 9 = (x+ 3)^2

however, since you add 9, you need to subtract 9 too, so that you do NOT change the original value (because 9 - 9 = 0)

so x^2 + 6x - 2 = (x^2 + 6x + 9) - 2 - 9

does that make sense?

Answer 4

i understand the second half. I guess I've never understood the perfect square part. Why 9 and not a different number? Thanks by the way :)

Answer 5

are you familiar with completing the square method?

Answer 6

if you have x^2 - 6x <--you look at the coefficient of x. In this case, the coefficient of x is 6. Divide that by 2 <--that becomes 3. Now square it <--that becomes 9 <---that's why it's 9

for example you have x^2 + 4x <--this will become x^2 + 4x + 4 <--because 4/2 is 2 then square of 2 is 4

x^2 + 10x <--this will become x^2 + 10x + 25 <--because 10/2 is 5 then square of 5 is 25

making sense now?

Answer 7

i meant to write x^2 + 6x not x^2 - 6x in the above explanation

Answer 8

yes!!!!!! Thank you sooooo much now everthing is clear! I've never had that explained to me so clearly!! :D

Answer 9

haha lol. w3elcome

Answer 10

welcome*

Answer 11

Hi I'm lost again! So I need to find the vertex of 3x^2 - 18x + 24 and so far I got 3(x+9)^(2) + 57 Can you tell me what I did wrong? @igbasallote

Answer 12

LGBASALLOTE* not ig

Answer 13

and i do not know much about vertices of parabolas without using calculus. sorry

Answer 14

ohhh and okay thanks