Question

what is a altitude and how do you find it on a isosceles triangle with a base of 10 and congruent sides of 9

Answer 1

The altitude is the line that is perpendicular to the base. In this case, since the two sides are congruent, the altitude bisects the triangle, which means that you have two congruent, right triangles.
You can apply pythagorean's theorem \[a^2+b^2=c^2\] to solve for the altitude.
NOTE: the base of each of the triangle is half of the big triangle because it is bisected