You have enough information to get the equations of the sides as lines, and you know the highest point. That is all you need. Split that tringle into 2 equal triangles and use trigonometery to get the angles, the length of the sides can be had by the pythagorean thereom. Although neither is really needed.
When you get a point, to
test it, if the first value(absolute value) is greater then half the length of the base, you know it is outside the triangle and can return false with no further calculations. Same thing with the height and y-point. With both of those tests true, you know it might be inside the triangle. Now you have to check the y-value. To do that, get the y value of the side of the x-value of the point you are testing. If the point you are testing is less then or equal to the y(absolute value again) point on the triangle, then it is inside.
example: the triangles 2 points on the base are(-6,0) and (6,0), h=10. And the point you are looking at is (-7,6). |-7| > length/2, so that point is outside the triangle.
Same triangle but looking at point (3,5). 3 < 6 so you have to test the y values. 5 < height, so it might be inside. You know the points of the side, use the point slope formula: y-y1=m(x-x1), where m is the slope or you can use the slope intercept equation y=mx+b where b is the y-intersection(10 in this case). m = (10-0)/(0-6)=-5/3. So y = (-5/3)x + 10. Plug in 3 for x and you have 5. The point you are testing is (3,5) so compare that y-value with the point found with the slope intercept equation, which is 5 in this case, which is right on the line, and probably inside the triangle, depending on the requirements. This is assuming no math errors on my part, which is a rather large assumption.
To convert it to a suitable algorithm, do it yourself on paper a few times to get a feel for it, and then transfer each step to code.
[ March 22, 2006: Message edited by: Rusty Shackleford ]