Question

Help please!
If the vertex of a parabola is (-1.5, -12.5), and its y-intercept is (0, -8). What are the x-intercepts of the parabola? anyone?

Answer 1

@lsherron can you help please?

Answer 2

0 is the x int and -8 is the y int

Answer 3

(0,-8) is the y intercept

Answer 4

The x intercepts are 2 of these below
(-2,0) (-1,0)
(-4,0) (2,0)
(2,0) (1,0)
(4,0) (-2,0)

Answer 5

(-2,0)

Answer 6

for both of them? I have to pick two

Answer 7

can I write this into an equation to check the vertex?

Answer 8

yes

Answer 9

can u show me

Answer 10

ok

Answer 11

thanks

Answer 12

@TheSmartOne

Answer 13

@jim_thompson5910 can you help me please?

Answer 14

If we write our equation in completed square form using coefficients a and b, which we want to find, then we have this:\[y=(x+a)^2+b\]Using the two coordinates we have: (-1.5, -12.5) and (0, -8):\[-8=(0+a)^2+b\]\[-8=a^2+b\]
\[-12.5=(-1.5+a)^2+b\]\[-12.5=2.25-3a+a^2+b\]Substituting what we found above into this:\[-12.5=2.25-3a+(a^2+b)\]\[-12.5=2.25-3a-8\]\[3a=6.75\]\[a=2.25\]
Using this in the equation:
\[-8=a^2+b=2.25^2+b=5.0625+b\]\[b=-13.0625\]
Giving us the answer:
\[y=(x+2.25)^2-13.0625\]

Answer 15

thank you but does this show me the x intercepts?

Answer 16

Oops sorry, misread the question. The x intercepts are when y=0, so set y=0 and solve for x. I'll help if you get stuck, but I imagine you can do this.