Can someone help me with this question please??

Original post by DenizS

Hi, I'm really stuck on this question, could someone please help?

Expand the following into the general form y=ax^2+bx+c

y=-1/2(x+2)^2 2-6

The answer is said to be y=-1/2^2-4x-14
How do they get this?

Expand

(x+2)^2=(x+2)(x+2)

and simplify to get it into the wanted form.

Reply 2

Original post by RDKGames

Expand

(x+2)^2=(x+2)(x+2)

and simplify to get it into the wanted form.

I still don't know how to get the answer though

Reply 3

Original post by DenizS

I still don't know how to get the answer though

You wrote out either the question wrong, or the answer. Also show your working, you need to have

x^2

and an

x

terms in there so you need to expand the brackets.

Reply 4

Original post by RDKGames

You wrote out either the question wrong, or the answer. Also show your working, you need to have

x^2

and an

x

terms in there so you need to expand the brackets.

I've written down the question and answer exactly how the worksheet has.

Reply 5

Original post by DenizS

I've written down the question and answer exactly how the worksheet has.

What's this then??? The 2-6?

Original post by DenizS

y=-1/2(x+2)^2 2-6

Reply 6

the bear

Original post by DenizS

I've written down the question and answer exactly how the worksheet has.

could you post a pic of the sheet ? *

Reply 7

beth-robinson99

Original post by RDKGames

What's this then??? The 2-6?

I was wondering the same??? otherwise i'd give it a shot hahaha :s-smilie:

Reply 8

Original post by beth-robinson99

I was wondering the same??? otherwise i'd give it a shot hahaha :s-smilie:

I want to say it's supposed to be +2(-6) which would fit the 14 constant after expansion of (x+2)², but the coefficient of x would be wrong.

Reply 9

beth-robinson99

y=-1/2(x+4)^2 2-6

The answer is said to be y=-1/2x^2-4x-14

-0.5(x+4)^2 = -0.5(x^2+8x+16) =-0.5x^2 - 4x - 8

so whatever the 2-6 is must make the -8 to -14? is it just meant to be -6?

Reply 10

Original post by DenizS

Anyway, your actual question is

y=-\frac{1}{2}(x+4)^2-6

which is equal to

y=-\frac{1}{2}x^2-4x-14

as required. Just expand the brackets and manipulate it from there. Do you know how to do that?

(edited 7 years ago)

Reply 11

Original post by RDKGames

Anyway, your actual question is

y=-\frac{1}{2}(x+4)^2-6

which is equal to

y=-\frac{1}{2}x^2-4x-14

as required. Just expand the brackets and manipulate it from there. Do you know how to do that?

You only need to put the expression into the form y= ax^2 + bx + c

I just don't know how you got from the first expression to -1/2x^2-4x-14

Reply 12

Original post by DenizS

You only need to put the expression into the form y= ax^2 + bx + c

I just don't know how you got from the first expression to -1/2x^2-4x-14

But that's what I'm saying you need to do, you need to expand the brackets first!

Reply 13

beth-robinson99

Original post by DenizS

You only need to put the expression into the form y= ax^2 + bx + c

I just don't know how you got from the first expression to -1/2x^2-4x-14

look at my comment above here somewhere, i showed you how to do it?
expand brackets out
half it
-6

Reply 14

Original post by RDKGames

But that's what I'm saying you need to do, you need to expand the brackets first!

-1/2(x^2 +8x+ 16) 2-6

Reply 15

Original post by beth-robinson99

y=-1/2(x+4)^2 2-6

The answer is said to be y=-1/2x^2-4x-14

-0.5(x+4)^2 = -0.5(x^2+8x+16) =-0.5x^2 - 4x - 8

so whatever the 2-6 is must make the -8 to -14? is it just meant to be -6?

I don't get why your answer is 6. I know how you worked it out, but that isn't the answer on the worksheet?

Reply 16

Original post by DenizS

-1/2(x^2 +8x+ 16) 2-6

Correct expansion but.... why did you keep the "2-6" when you clearly made a typo on it??????

It should just be -6 after the bracket. Now multiply everything in the bracket by -1/2 and simplify.

Reply 17