trigonometric function

Basic relationship

Type:

1+(tana)^2=(seca)^2= 1/(cosa)^2= 1/[ 1-(sina)^2]

In this problem, because tana = 3 >；; 0 and a are a triangle.

inner angle

, so a is an acute angle,

A's

Trigonometric function value

Are positive, so I found Sina.