Question

Trigonometry

Angle Sum and Difference, Double Angle and Half Angle Formulas
Find the exact value of:
Sin 85* cos 20* - Cos 85* sin 20*

Answer 1

sin(105)

Explanation:

Apply the trig identity: sinAcosB+cosAsinB = sin(A+B)

integrating that into the question to find A and B

sin(85)cos(20)+cos(85)sin(20)

= sin(85+20) = sin(105)