Question

Tính:

a) \(\cos^212+\cos^278+\cos^21+\cos^289\)

b) \(\sin^23+\sin^215+\sin^275+\sin^287\)

c) \(\sin^21+\sin^22+\sin^33+...+\sin^288+\sin^289\)

Answer 1

b) \(sin^23^o+sin^215^o+sin^275^o+sin^287^o\)

\(=\left(sin^23^o+cos^23^o\right)+\left(sin^215^o+cos^215^o\right)\)

\(=1+1=2\)

Answer 2

a) \(cos^212^o+cos^278^o+cos^21^o+cos^289^o\)

\(=\left(sin^278^o+cos^278^o\right)+\left(sin^289^o+cos^289^o\right)\)

\(=1+1=2\)