# solving a equation

• May 5th 2012, 12:35 AM
davellew69
solving a equation
hi would I solve equations such as

y=-3x+2

and

y=2x^2-7x-4

by factorising or using the quad formula, as I need to find where the above intersect on a graph.

Many thanks

Dave
• May 5th 2012, 12:55 AM
biffboy
Re: solving a equation
Quote:

Originally Posted by davellew69
hi would I solve equations such as

y=-3x+2

and

y=2x^2-7x-4

by factorising or using the quad formula, as I need to find where the above intersect on a graph.

Many thanks

Dave

At intersection 2x^2-7x-4= -3x+2 So 2x^2 -4x -6=0 Divide both sides by 2 giving x^2-2x-3=0 Now factorize and get two values for x.
Sub these back into y= -3x+2 to get the corresponding values of y.
• May 5th 2012, 05:47 AM
BobtheBob
Re: solving a equation
This is just a simple simultaneous equation. There will of course be 2 intersection points. $\displaystyle y=2x^2-7x-4$ is a parabola and $\displaystyle y=-3x+2$ will intersect it at 2 points.

as $\displaystyle y=y$ then $\displaystyle 2x^2-7x-4=-3x+2$

Therefore, $\displaystyle 2x^2-7x-4=-3x+2=2x^2-4x-6$

$\displaystyle \frac{2x^2-4x-6}{2} = x^2-2x-3$

This is a quadratic, so factorise this equation and it will give you two points for $\displaystyle x$. Put these back into the equation, and you will retrive the values for $\displaystyle y$.