Write the product as a sum or difference of trigonometric functions.
-$\cos 36 ^ { \circ } \sin 21 ^ { \circ }$
A) $\frac { 1 } { 2 } \left( \cos 57 ^ { \circ } + \cos 15 ^ { \circ } \right)$
B) $\frac { 1 } { 2 } \left( \sin 57 ^ { \circ } - \sin 15 ^ { \circ } \right)$
C) $\frac { 1 } { 2 } \left( \cos 57 ^ { \circ } - \cos 15 ^ { \circ } \right)$
D) $\frac { 1 } { 2 } \left( \sin 57 ^ { \circ } + \sin 15 ^ { \circ } \right)$

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The Answer of Write the product as a sum or difference of trigonometric functions.
-$\cos 36 ^ { \circ } \sin 21 ^ { \circ }$
A) $\frac { 1 } { 2 } \left( \cos 57 ^ { \circ } + \cos 15 ^ { \circ } \right)$
B) $\frac { 1 } { 2 } \left( \sin 57 ^ { \circ } - \sin 15 ^ { \circ } \right)$
C) $\frac { 1 } { 2 } \left( \cos 57 ^ { \circ } - \cos 15 ^ { \circ } \right)$
D) $\frac { 1 } { 2 } \left( \sin 57 ^ { \circ } + \sin 15 ^ { \circ } \right)$

Write the Product as a Sum or Difference of Trigonometric cos⁡36∘sin⁡21∘\cos 36 ^ { \circ } \sin 21 ^ { \circ }cos36∘sin21∘

Write the Product as a Sum or Difference of Trigonometric $\cos 36 ^ { \circ } \sin 21 ^ { \circ }$