# If cotx= -3/4 and 90<x<180, what is sinx?

##### 1 Answer
May 10, 2015

Use the trig identity:

${\sin}^{2} x = \frac{1}{1 + {\cot}^{2} x} = \frac{1}{1 + \frac{9}{16}} = \frac{16}{25} - \to \sin x = \pm \frac{4}{5} = \pm 0.8$

Since 90 < x < 180, and x is in Quadrant II, then sin x is positive -> sin x = 0.8