Use a calculator to decide whether the statement is true or false.
-$$\cos \left( 2 \cdot 90 ^ { \circ } \right) = \cos ^ { 2 } 90 ^ { \circ } - \sin ^ { 2 } 90 ^ { \circ }$$
A) True
B) False

Question

Quizplus · Accepted Answer

The statement is true because it is an application of the double angle formula for cosine, which states that $\cos(2\theta) = \cos^2\theta - \sin^2\theta$. For $\theta = 90^\circ$, $\cos(180^\circ) = -1$, $\cos(90^\circ) = 0$, and $\sin(90^\circ) = 1$, so the equation simplifies to $-1 = 0 - 1$, which is true.

Use a Calculator to Decide Whether the Statement Is True cos⁡(2⋅90∘)=cos⁡290∘−sin⁡290∘\cos \left( 2 \cdot 90 ^ { \circ } \right) = \cos ^ { 2 } 90 ^ { \circ } - \sin ^ { 2 } 90 ^ { \circ }cos(2⋅90∘)=cos290∘−sin290∘

Use a Calculator to Decide Whether the Statement Is True $\cos \left( 2 \cdot 90 ^ { \circ } \right) = \cos ^ { 2 } 90 ^ { \circ } - \sin ^ { 2 } 90 ^ { \circ }$