Evaluate the expression using the concept of a reference angle. $\cos \left( - 675 ^ { \circ } \right)$
A) $- \frac { \sqrt { 2 } } { 2 }$
B) $\frac { \sqrt { 2 } } { 2 }$
C) $\frac { \sqrt { 2 } } { 6 }$
D) $- \frac { \sqrt { 6 } } { 2 }$
E) $\frac { \sqrt { 6 } } { 6 }$

Question

Quizplus · Accepted Answer

First, find the equivalent positive angle by adding 360 degrees until the angle is positive: -675 + 720 = 45 degrees. The reference angle for 45 degrees is 45 degrees itself, and $\cos(45^\circ) = \frac{\sqrt{2}}{2}$.

Evaluate the Expression Using the Concept of a Reference Angle cos⁡(−675∘)\cos \left( - 675 ^ { \circ } \right)cos(−675∘)

Evaluate the Expression Using the Concept of a Reference Angle $\cos \left( - 675 ^ { \circ } \right)$