Question

Find the equation of the quadratic function with zeros 10 and 12 and vertex at (11, -2).

y = 2x2 - 44x + 120

y = 2x2 - 44x - 240

y = 2x2 - 44x + 240

y = -2x2 - 44x + 240
im thinking its either the last one or second the the last one.

Answer 1

vertex form is
a(x - h)^2 + k

where (h,k) are the coordinates the the vertex

Answer 2

and a is a number to be found

Answer 3

how do i find it?

Answer 4

so here h = 11 and k = -2

Answer 5

y = a(x - 11)^2 - 2

plug in one of the zeroes say y = 0 and x = 10 and solve for a

Answer 6

0=a(10-11)^2-2
0=-1a
a=0

Answer 7

your secon ine is wrong

Answer 8

(10-11)^2 = -1^2 = 1

Answer 9

okay.

Answer 10

0 = a - 2
a = 2

Answer 11

so now you need to expand
y = 2(x - 11)^2 - 2

Answer 12

and that is done by..?
sorry...i rly dont get this stuff..

Answer 13

2(x - 11)^2 - 2
= 2[x^2 -22x + 121] - 2

can you continues

Answer 14

multiply each term in the parentheses by 2

Answer 15

oh okay i see!

Answer 16

so now i expand it

Answer 17

yes

Answer 18

2(x-11) (x-11)-2

Answer 19

@welshfella

Answer 20

no
you just multiply 2x^2 - 22x + 121 by 2 then take 2 away

Answer 21

what? im sorry im confused

Answer 22

- ive worked out (x - 11)(x - 11) already

Answer 23

(x - 11)(x - 110 = x^2 - 22x + 121

Answer 24

* 11) not 110

Answer 25

okay.. so i multiply the whole thing by 2?

Answer 26

yes -then take 2 away

( the -2 at the end)

Answer 27

4x^2-44x+242. now subract 2 from each number?

Answer 28

no - just from the 242

you can only subtract like terms

Answer 29

4x2-44+240

Answer 30

then take away a 2?

Answer 31

oh its 2*x2 = 2x^2 not 4x^2

Answer 32

okay i was gonna say. lol everything else matches but the 4x lol

Answer 33

2x^2 - 44x + 242 - 2
= 2x^2 - 44x + 240

Answer 34

got it! so i was close, i had a feeling it be that one or the last one.