Toán chứng minh (1-sin2a)/(1+sin2a)=cot^2(pi/4+a) 12/09/2021 By Eden chứng minh (1-sin2a)/(1+sin2a)=cot^2(pi/4+a)
$VP=\dfrac{\cos^2\Big(\dfrac{\pi}{4}+a\Big) }{\sin^2\Big(\dfrac{\pi}{4}+a\Big)}$ $=\dfrac{1+\cos\Big(\dfrac{\pi}{2}+2a\Big) }{1-\cos\Big(\dfrac{\pi}{2}+2a\Big) }$ $=\dfrac{1-\sin2a}{1+\sin2a}$ $=VT$ Trả lời
$VP=\dfrac{\cos^2\Big(\dfrac{\pi}{4}+a\Big) }{\sin^2\Big(\dfrac{\pi}{4}+a\Big)}$
$=\dfrac{1+\cos\Big(\dfrac{\pi}{2}+2a\Big) }{1-\cos\Big(\dfrac{\pi}{2}+2a\Big) }$
$=\dfrac{1-\sin2a}{1+\sin2a}$
$=VT$
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