Áp dụng 2 công thức: \(sina=cos\left(90^0-a\right)\) và \(sin^2a+cos^2a=1\)
A.
\(=cos^211+cos^238+sin^2\left(90-52\right)+cos^2\left(90-79\right)\)
\(=cos^211+cos^238+sin^238+sin^211\)
\(=sin^211+cos^211+sin^238+cos^238=1+1=2\)
B.
\(=sin^215+sin^235+sin^245+cos^2\left(90-55\right)+cos^2\left(90-75\right)\)
\(=sin^215+cos^215+sin^235+cos^235+\left(\dfrac{\sqrt{2}}{2}\right)^2\)
\(=1+1+\dfrac{1}{2}=\dfrac{5}{2}\)
Đúng 2
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