Angle Sum Formula

These formulas allow you to express the exact value of trigonometric expressions that you could not otherwise express. Consider the sin(105°). Unlike the sin(30) which can be expressed as ½, the sin(105) cannot simply be represented as a rational expression. However, the angle sum formula allows you to represent the exact value of this function

USe the angle sum formula to determine the exact value of cos(75°)

Answer

Since 75° = 30° + 45° we can use our formula to rewrite

cos(75) as cos(30° + 45°)

USe the angle sum formula to determine the exact value of sin(75°)

Answer

Since 75° = 30° + 45° we can use our formula to rewrite

sin(75) as sin(30° + 45°)

USe the angle sum formula to determine the exact value of cos(105°)

Answer

Since 105° = 60° + 45° we can use our formula to rewrite

cos(105) as cos(60° + 45°)