# find the value of a in coordinate

• Dec 8th 2012, 08:47 PM
rcs
find the value of a in coordinate
triangle ABC has its coordinates at A(a, -1) , B(8,-1) , C(5,4). If the base is twice the
height, find a.

can anybody do me a favor on this problem...

thanks a lot
• Dec 9th 2012, 12:10 AM
MarkFL
Re: find the value of a in coordinate
If we assume the base lies along the line $y=-1$, then what is the vertical distance (the altitude of the triangle) from point $C$ to this line?

Once you find the altitude, then what are the $x$-coordinates of the two points on the base line whose distance from point $B$ is twice the altitude?
• Dec 9th 2012, 12:15 AM
BobP
Re: find the value of a in coordinate
I suppose the base is intended to be AB, (but it depends on which way you choose to look at it, a badly worded question), so, since A and B have the same y coordinate, the base length will be the difference between their x coordinates.
Also, since A and B have the same y coordinate, it's easy to work out the height of the triangle.
All that's left is to say the base length is double the height and to solve the resulting equation.
• Dec 9th 2012, 02:59 AM
rcs
Re: find the value of a in coordinate
Quote:

Originally Posted by BobP
I suppose the base is intended to be AB, (but it depends on which way you choose to look at it, a badly worded question), so, since A and B have the same y coordinate, the base length will be the difference between their x coordinates.
Also, since A and B have the same y coordinate, it's easy to work out the height of the triangle.
All that's left is to say the base length is double the height and to solve the resulting equation.

According to the book where I got this problem has answer but does not have solution, that is why I'm wondering how this a = -2 from the book.

Hope you understand. Help me understand how to solve in getting a = -2.

Thanks
• Dec 9th 2012, 03:03 AM
MarkFL
Re: find the value of a in coordinate
There is another solution as well, and both are easily found if you follow my suggestion above.