Quadratic function probelm

**Paymemoney** · March 26th 2010, 01:34 AM

Hi
Need help on the following question:
1) A straight line with gradient 2 passes through the vertex of the parabola $y= x^2-5x+3$ . What is the equation to the line?

P.S

**Grandad** · March 26th 2010, 03:43 AM

Hello Paymemoney

Originally Posted by Paymemoney

Hi
Need help on the following question:
1) A straight line with gradient 2 passes through the vertex of the parabola $y= x^2-5x+3$ . What is the equation to the line?

P.S

I don't know what method you use for finding the vertex of a parabola, but you can complete the square:

$y= x^2-5x+3$

$=\left(x-\frac52\right)^2 -\frac{25}{4}+3$

$=(x-2.5)^2 -3.25$

So the vertex is at $(2.5, -3.25)$ . Now use

$y -y_1 = m(x-x_1)$

to find the equation of the line.

Can you complete it now?

Grandad

**Paymemoney** · March 26th 2010, 03:56 AM

Originally Posted by Grandad

Hello PaymemoneyI don't know what method you use for finding the vertex of a parabola, but you can complete the square:

$y= x^2-5x+3$

$=\left(x-\frac52\right)^2 -\frac{25}{4}+3$

$=(x-2.5)^2 -3.25$

So the vertex is at $(2.5, -3.25)$ . Now use

$y -y_1 = m(x-x_1)$

to find the equation of the line.

Can you complete it now?

Grandad

thank you i understand now.

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