# Quadratic formula questions

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• August 8th 2010, 09:51 PM
GAVREED2
Quadratic formula questions
Can someone help me solve these questions i'm finding it really difficult.....

SIMULTANEOUS EQUATION

2x+y=7
3x-y=3

SOLVE ALGEBRAICALLY

(a) y= x^2 + 3x -8
y= x - 5

(b) Write down the formula to find the roots of the equation
(c) Use the formula to find the roots of: 3x^2-9x-16=0
• August 8th 2010, 09:59 PM
pickslides
Quote:

Originally Posted by GAVREED2

2x+y=7
3x-y=3

$2x+y=7$ ...(1)
$3x-y=3$ ...(2)

Using (1) $2x+y=7\implies y = 7-2x$ and subbing this into (2)

$3x-(7-2x)=3$ Can you finish it?

Quote:

Originally Posted by GAVREED2
.....

SOLVE ALGEBRAICALLY

(a) y= x^2 + 3x -8
y= x - 5

$y=y$

$x^2 + 3x -8=x-5$

$x^2 + 2x -3= 0$

Can you have a go from here? (if not my answer to the next question might help!)

Quote:

Originally Posted by GAVREED2
(c) Use the formula to find the roots of: 3x^2-9x-16=0

For $ax^2+bx+c=0\implies x = \frac{-b\pm\sqrt{b^2-4ac}}{2a}$