Question

cos75-cos15

Answer 1

\[\cos(u)-\cos(v)=-2\sin\left(\frac{u+v}2\right)\sin\left(\frac{u-v}2\right)\]

Answer 2

\[cos 75=0.258819045-cos 15=0.965925826\]
=-0.707106781

Answer 3

as given above
\[\cos 75-\cos 15=-2\sin \frac{ 75+15 }{ 2 }\sin \frac{ 75-15 }{ 2 }=-2\sin 45 \sin 30\]
\[=- 2*\frac{ 1 }{ \sqrt{2} }*\frac{ 1 }{ 2 }=-\frac{ 1 }{ \sqrt{2} }=-\frac{ \sqrt{2} }{ 2 }=?\]