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Hi can someone help with this maths question

The graph shows the curve y=ax²+bx+c and it has a maximum point of (2,3) and a passes through (0,-5)
So far I've done...
(X-1)(X-3)
Then, I completed the square and got (x-2)²-1 but I don't know if I did it right or what to do next
Okay... I suppose you want to find the actual quadratic.

I can't follow, from the info given, what do you mean by "(x-1)(x-3)"?
Also, can you use calculus? (P.S. You really don't need it, but some people prefer calculus, so I'd ask just in case)
(edited 6 months ago)
Reply 2
Original post by tonyiptony
Okay... I suppose you want to find the actual quadratic.

I can't follow, from the info given, what do you mean by "(x-1)(x-3)"?
Also, can you use calculus? (P.S. You really don't need it, but some people prefer calculus, so I'd ask just in case)

No I cant use calculus, the topic is quadratic functions
Original post by Bird1234
No I cant use calculus, the topic is quadratic functions


Okay. No calculus then. Completing square is a good idea, but think of it in reverse.

Do you know how to relate the completed square form, y=a(x-h)^2+k, to the turning point of the quadratic?
Reply 4
Yes from your example that would be (h,k)
Original post by Bird1234
Yes from your example that would be (h,k)


Good, now from the info given from the question, you know "h" and "k" of the quadratic in completed square form.
What you don't know is "a"... what else have you not used?

We are practically done.
(edited 6 months ago)
Reply 6
Original post by tonyiptony
Good, now from the info given from the question, you know "h" and "k" of the quadratic in completed square form.
What you don't know is "a"... what else have you not used?

We are practically done.

The (0,-5) maybe
Original post by Bird1234
The (0,-5) maybe


Yeah, can you complete the problem now? You should be able to do this.

Just in case you don't know how (0, -5) comes into play...

Spoiler

Reply 8
Original post by tonyiptony
Yeah, can you complete the problem now? You should be able to do this.

Just in case you don't know how (0, -5) comes into play...

Spoiler


I did this
(x-2)²+3
But when I expand it, the y intercept is 7 not -5
(edited 6 months ago)
Original post by Bird1234
I did this
(x-2)²+3
But when I expand it, the y intercept is 7 not -5


Ah, common error here.
(x-2)²+3 is not a sentence - it's missing a verb (always be mindful writing maths is nothing different than writing english, it's just muddled with symbols).
In this case, it's the equal sign.

Well, what does (x-2)²+3 equal to? Is it really 0? Reread #4 carefully.
Reply 10
Original post by tonyiptony
Ah, common error here.
(x-2)²+3 is not a sentence - it's missing a verb (always be mindful writing maths is nothing different than writing english, it's just muddled with symbols).
In this case, it's the equal sign.

Well, what does (x-2)²+3 equal to? Is it really 0? Reread #4 carefully.

I'm sorry I'm very confused
Original post by Bird1234
I'm sorry I'm very confused

It's fine.

At this point, at best we can say the quadratic is in the form y=a(x-2)^2+3 (reread #4, there's an "a" in front to be found).

Recall from #6 that we only know h=2 and k=3. We don't know what "a" is.
You (unintentionally) assumed it's 1, which isn't always the case.
Also remember (0,-5) was not used? It's not meant to be used as double-checking, it actually gives information (on what "a" is).

P.S. Problems are often structured such that you need every single piece of information given with no extras. That is, no more, and no less.
(edited 6 months ago)
Reply 12
Original post by tonyiptony
It's fine.

At this point, at best we can say the quadratic is in the form y=a(x-2)^2+3 (reread #4, there's an "a" in front to be found).

Recall from #6 that we only know h=2 and k=3. We don't know what "a" is.
You (unintentionally) assumed it's 1, which isn't always the case.
Also remember (0,-5) was not used? It's not meant to be used as double-checking, it actually gives information (on what "a" is).

P.S. Problems are often structured such that you need every single piece of information given with no extras. That is, no more, and no less.

Ok how would u do that because I get this part
(X-2)²+3
X²-4x+7
But what can a be that would give -5
Sorry for taking so long to understand but I have no clue how to work out the a part
Original post by Bird1234
Ok how would u do that because I get this part
(X-2)²+3
X²-4x+7
But what can a be that would give -5
Sorry for taking so long to understand but I have no clue how to work out the a part

Again, at best we know it's y=a(x-2)²+3, not y=(x-2)²+3!
Do actually copy down the whole thing, don't skip anything (i.e. don't forget the "y=" and the "a").
Then proceed with using (0,-5) by...

Spoiler


P.S. A good solution structure, at least from my habit of doing maths, would look a bit like this...

Spoiler

(edited 6 months ago)
Reply 14
Original post by tonyiptony
Again, at best we know it's y=a(x-2)²+3, not y=(x-2)²+3!
Do actually copy down the whole thing, don't skip anything (i.e. don't forget the "y=" and the "a").
Then proceed with using (0,-5) by...

Spoiler


P.S. A good solution structure, at least from my habit of doing maths, would look a bit like this...

Spoiler


OK thanks

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