# Useful Formulae

10 TRIGONOMETRY applied to right triangles A right triangle with sides of length a,b,c, and angle is shown opposite left. The six trigonometric functions sine, cosine, tangent, cosecant,secant and cotangent are then defined as follows sin cos tan csc sec cot The sine and cosine are the height and base of a right triangle in a circle of radius 1 as shown below and opposite top right. a cos and bsin By PythagorasTheorem see page 2 we know a2 b2 c2,hence for any angle in the circle we have the important identity cos2 sin2 1 Sines, cosines and tangents have positive or negative values in different quadrants of the circle as shown below right. a c b a c b b c c a a b 11