a: \(A=sin^279^0+cos^279^0=1\)
b: \(B=tan73^0\cdot tan37^0\cdot tan53^0\cdot tan17^0\)
\(=tan73^0\cdot tan17^0\cdot tan37^0\cdot tan53^0\)
\(=tan73^0\cdot cot73^0\cdot tan37^0\cdot cot37^0=1\cdot1=1\)
c: \(C=cos^273^0+cos^253^0+cos^217^0+cos^237^0\)
\(=\left(cos^273^0+cos^217^0\right)+\left(cos^253^0+cos^237^0\right)\)
\(=\left(sin^273^0+cos^273^0\right)+\left(sin^253^0+cos^253^0\right)\)
=1+1=2
d: \(D=sin59+cos59-sin31-cos31\)
=cos31+sin31-sin31-cos31
=0-0=0
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