Year 12s: what will be the first way you research your future options? >>

Year 12s: what will be the first way you research your future options? >>

Year 12s: what will be the first way you research your future options? >>

AS level coordinate geometry

The curve C has the equation:
y=x^2 + ax + b,

where a and b are constants.

Given that the minimum point of C has coordinates (-2, 5), find the values of a and b.

How would i go about doing this?

Using completing the square

Do you know how

(x-p)^2 + q

relates to the turning point

I am assuming that you have not learnt differentiation yet

OP

Original post by TenOfThem

Using completing the square

Do you know how

(x-p)^2 + q

relates to the turning point

I am assuming that you have not learnt differentiation yet

I have, i solved it by differentiation dy/dx = 2x + a, a = 4 then sub to get b = 9, but in the mark scheme it's only showing the completing the square method, which i've never been taught. Though the answers are still correct...

What's your query then?

OP

Original post by ViralRiver

What's your query then?

How do you solve it by completing the square.

Original post by lemonpwns1

How do you solve it by completing the square.

Well

y = (x-p)^2 + q

Has a turning point at (p,q)

So ... if you expand this (having put your minimum point in for p and q) you can equate to find a and b

OP

Original post by TenOfThem

Well

y = (x-p)^2 + q

Has a turning point at (p,q)

So ... if you expand this (having put your minimum point in for p and q) you can equate to find a and b

Thank you, do you know if this is in the C1 book, because im looking through it and cant seem to find anything on it. Thanks again.

Which C1 book?

Edexcel it is chapter 2

(edited 12 years ago)

OP

Original post by TenOfThem

Which C1 book?

Edexcel it is chapter 2

Edexcel yes, but i know how to complete the square, just not how to relate it to graphs, which isn't in chapter two.

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