# Question on quadratic and linear equation/graph

• Sep 26th 2011, 11:15 AM
FailInMaths
Question on quadratic and linear equation/graph
http://i1099.photobucket.com/albums/.../Photo0015.jpg

Additional Information: The curve of y=(4-x)(x+5) cuts the x-axis at A and B. A straight line cuts the curve at A and at C. The x-coordinate of C is 2. Find
(a) the coordinates of point C,
(b) the equation of line AC,
(c) the area of Triangle ABC

I am stuck at the (a) part. I can't find a solution to get the "y" of point C. I don't see any clue too. What should I do to get "y" of point C?
• Sep 26th 2011, 11:58 AM
Ross137
Re: Question on quadratic and linear equation/graph
Point C is on the curve of equation y = (4-x)(x+5) so as you know the x co-ordinate you can simply sub it into the equation of the curve to find the y co-ordinate.
• Sep 26th 2011, 12:00 PM
Re: Question on quadratic and linear equation/graph
The y co-ordinate of Point C is

$y=(4-x)(x+5)=f(2)$

when x=2

as C is on both the line and curve.
• Sep 29th 2011, 07:22 AM
FailInMaths
Re: Question on quadratic and linear equation/graph
Quote:

The y co-ordinate of Point C is

$y=(4-x)(x+5)=f(2)$

when x=2

as C is on both the line and curve.

Quote:

Originally Posted by Ross137
Point C is on the curve of equation y = (4-x)(x+5) so as you know the x co-ordinate you can simply sub it into the equation of the curve to find the y co-ordinate.

Thanks, sorry for the late reply, I got it. =)