In triangle ABC, angle C = 90 degrees, angle A = 60 degrees, AB = 36. Find the AC.

A triangle is three points that do not lie on one straight line, connected by segments. In this case, the points are called the vertices of the triangle, and the segments are called its sides.
A rectangular triangle is a triangle in which one corner is a straight line (equal to 90º). The side opposite the right angle is called the hypotenuse, and the other two are called legs.
To calculate the AC leg, we use the cosine theorem. The cosine of an acute angle of a right triangle is the ratio of the adjacent leg to the hypotenuse:
cos A = AC / AB;
AC = AB · cos A;
cos 60º = 1/2;
AC = 36 1/2 = 36/2 = 18 cm.
Answer: the length of the AC leg is 18 cm.