Question

Tinh:

\(A=cos^220^o+cos^230^o+...+cos^270^o.\)

\(B=sin^25^o+sin^225^o+sin^245^o+sin^265^o+sin^285^o.\)

jup mk vs 

Answer 1

k mk đi

ai k mk

mk k lại

thanks

Answer 2

deo tra loi thoi m vo chat linh tinh ak

Answer 3

ap dung \(\sin a=\cos b\)

va ap dung\(sin^2a+cos^2a=1\)

Answer 4

\(A=\cos^220^o+\cos^230^o+\cos^240^o+\cos^250^o+\cos^260^o+\cos^270^o\)

\(A=\sin^270^o+\sin^260^o+\sin^250^o+\cos^250^o+\cos^260^o+\cos^270^o\)

\(A=\left(\sin^270^o+\cos^270^o\right)+\left(\sin^260^o+\cos^260^o\right)+\left(\sin^250^o+\cos^250^o\right)\)

\(A=1+1+1=3\)

Vậy ...

\(B=\sin^25^o+\sin^225^o+\sin^245^o+\sin65^o+\sin^285^o\)

\(B=\cos^285^o+\cos^265^o+\sin^245^o+\sin^265^o+\sin^285^o\)

\(B=\left(\cos^285^o+\sin^285^o\right)+\left(\cos^265^o+\sin^265^o\right)+\sin^245^o\)

\(B=1+1+\frac{1}{2}=\frac{5}{2}\)

Vậy ...