Area of triangle by integrals (is this right?)

1. Mar 10, 2008

silicon_hobo

[SOLVED] area of triangle by integrals (is this right?)

1. The problem statement, all variables and given/known data
Use integrals to find the area of a triangle with vertices (0,5),(-2,-2),(2,2).

2. Relevant equations

3. The attempt at a solution
I think I've got it. I'm just looking for some confirmation of my method before I move on.

http://www.mcp-server.com/~lush/shillmud/quest3.jpg

P.S. How do I add a [Solved] to the title?

Last edited: Mar 10, 2008
2. Mar 10, 2008

Dick

How are you getting e.g. integral of 5x/2+5 to be 5x^2/4+5x^2/2??

3. Mar 10, 2008

silicon_hobo

Ooops. Thanks for pointing that out Dick. I found the dx of 5x instead of the dx of 5 which interestingly seems not to have affected my answer. I guess you can see why I'm using the forum. Everything should be in order now. Cheers.

4. Mar 10, 2008

Dick

If you are still getting 20 for the area, I can't agree with that. Double check again.

5. Mar 10, 2008

silicon_hobo

Okay, I went through again and got A=10. When putting in values for x to solve I sub the rightmost value from the top of integral sign and then subtract from that the same antiderivative with the leftmost x value (top of the integral sign). This is correct? Thanks!

6. Mar 10, 2008

Dick

Yes, A=10 works.

7. Mar 10, 2008

silicon_hobo

Thanks Dick. Heron's method confirms it. Now how do I mark this one [SOLVED] ?

8. Mar 10, 2008

Dick

Under Thread Tools, at the top, isn't there a "Mark this thread as solved"?