Instead memorize values of sin, cos, tan and cot for 45° can them calculate. Draw the isosceles right triangle. Its angles equal 90°, 45°, 45°. Let triangle have legs of length 1. Length of hypotenuse calculate from Pythagorean theorem. Instead memorize values of sin, cos, tan and cot for 30° and 60° can them calculate. Draw the equilateral triangle and split by height into two right triangle. Angles of this right triangle equal 90°, 60°, 30°. Let length of side of the equilateral triangle equals 2. Lenght of height calculate from Pythagorean theorem.