Giải:
\(A=\sin10+\sin40-\cos50-\cos80\)
\(\Leftrightarrow A=\cos80+\cos50-\cos50-\cos80\)
\(\Leftrightarrow A=0\)
Vậy ...
\(B=\cos15+\cos25-\sin65-\sin75\)
\(\Leftrightarrow B=\sin75+\sin65-\sin65-\sin75\)
\(\Leftrightarrow B=0\)
Vậy ...
\(C=\dfrac{\tan27.\tan63}{\cot63.\cot27}\)
\(\Leftrightarrow C=\dfrac{\tan27.\tan63}{\tan27.\tan63}\)
\(\Leftrightarrow C=1\)
Vậy ...
\(D=\dfrac{\cot20.\cot45.\cot70}{\tan20.\tan45.\tan70}\)
\(\Leftrightarrow D=\dfrac{\cot20.\cot45.\cot70}{\cot70.\cot45.\cot20}\)
\(\Leftrightarrow D=1\)
Vậy ...
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