# Given the point P(-3/5, 4/5), how do you find sintheta and costheta?

Nov 5, 2016

#### Explanation:

Given any point A(x, y)

$x = \left(\sqrt{{x}^{2} + {y}^{2}}\right) \cos \left(\theta\right)$ and $y = \left(\sqrt{{x}^{2} + {y}^{2}}\right) \sin \left(\theta\right)$

In the case of point $P \left(- \frac{3}{5} , \frac{4}{5}\right)$, it is a happy coincidence that

$\sqrt{{\left(- \frac{3}{5}\right)}^{2} + {\left(\frac{4}{5}\right)}^{2}} = 1$

Therefore:

$- \frac{3}{5} = \cos \left(\theta\right)$ and $\frac{4}{5} = \sin \left(\theta\right)$