Use a graphing calculator to make a conjecture as to whether each equation is an identity.
-Find $\sin \theta$ if $\cos \theta = \frac { 2 } { 3 }$ and $\theta$ is in quadrant IV.
A) $- \frac { \sqrt { 5 } } { 3 }$
B) $\frac { 5 } { 4 }$
C) $- \frac { 3 } { 2 }$
D) $\frac { 3 \sqrt { 7 } } { 7 }$

Question

Quizplus · Accepted Answer

In the fourth quadrant, sine is negative, and using the Pythagorean identity $\sin^2 \theta + \cos^2 \theta = 1$, we find $\sin \theta = -\sqrt{1 - \cos^2 \theta} = -\sqrt{1 - \left(\frac{2}{3}\right)^2} = -\sqrt{1 - \frac{4}{9}} = -\sqrt{\frac{5}{9}} = -\frac{\sqrt{5}}{3}$.

Use a Graphing Calculator to Make a Conjecture as to Whether