# Math Help - Trig Function

1. ## Trig Function

The expression can be written in the form , where and .
Find the values of and . Give the value of , in radians, correct to three decimal places.

2. Hello,
Originally Posted by Haris
The expression can be written in the form , where and .
Find the values of and . Give the value of , in radians, correct to three decimal places.

You can take the problem from the bottom :
$A \sin(x+\phi)=A \left(\sin x\cos \phi+\cos x \sin \phi\right)=\cos(x) (A \sin \phi)+\sin(x) (A \cos \phi)$

Hence $A \sin \phi=3$ and $A \cos \phi=-4$
Can you solve it ?

Hint : in order to find A, square both equations and add them up, then use the identity cos²+sin²=1