In triangle ABC, angle C is 90, AC = 13, AB = 20. Find sin B.

Given: right-angled triangle ABC;
angle C = 90;
AC and BC – legs;
AB – hypotenuse;
AC = 13;
AB = 20.
Find: sine of angle B, that is, sin B -?
Decision:
Consider a rectangular ABC. The sine of the angle in a right-angled triangle is equal to the ratio of the opposite leg to the hypotenuse. Hence:
sin B = AC / AB (substitute 13 instead of AC, and 20 instead of AB);
sin B = 13/20.
Answer: sin B = 13/20.