Answer:
Step-by-step explanation:
An isosceles triangle is one that has 2 sides that are the same length, like ours here. Because of the Isosceles Triangle Theorem, if 2 side lengths are congruent, then the angles opposite those sides are congruent, as well. That means that both base angles are 53 degrees. However, we are looking for the altitude, or height, of the triangle. That changes everything. Drawing in the height serves to cut the triangle in half, splitting both the vertex angle (the angle at the top of the triangle) and the base exactly in half. Now we have 2 right triangles which are mirror images of each other. We only need concentrate on one of these triangles. What the triangle looks like now:
One base angle is 90 degrees and the other is 53 degrees. By the Triangle Angle-Sum Theorem, the third angle has to be a degree measure which ensures that all the angles add up to 180. Therefore, the third angle measures 180 - 90 - 53 = 37. Even still, besides knowing all the angle measures, we really don't need any besides the 53 degree one.
As far as side lengths go, the base is 12 (because the height cut it in half). To find a missing side in a right triangle you either use Pythagorean's Theorem or right triangle trig, depending upon the info you're given. We only have enough to use right triangle trig.
We have the base angle of 53, which is our reference angle, the side next to, or adjacent to, the reference angle, and we are looking for the side length opposite the reference angle. This is the tan ratio where
[tex]tan\theta=\frac{opp}{adj}[/tex] where tangent of the reference angle is equal to the side opposite the reference angle over the side adjacent to the reference angle. Filling in that ratio:
[tex]tan53=\frac{opp}{12}[/tex] and multiply both sides by 12 to get
12tan53 = opp and do this on your calculator to get that
opp = 15.9 inches
