1.若cos x=5/13 及tan(x+y)= -120/119,其中x及y为锐角.证明x=y.
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![1.若cos x=5/13 及tan(x+y)= -120/119,其中x及y为锐角.证明x=y.](/uploads/image/z/14919763-67-3.jpg?t=1.%E8%8B%A5cos+x%3D5%2F13+%E5%8F%8Atan%28x%2By%29%3D+-120%2F119%2C%E5%85%B6%E4%B8%ADx%E5%8F%8Ay%E4%B8%BA%E9%94%90%E8%A7%92.%E8%AF%81%E6%98%8Ex%3Dy.)
1.若cos x=5/13 及tan(x+y)= -120/119,其中x及y为锐角.证明x=y.
1.若cos x=5/13 及tan(x+y)= -120/119,其中x及y为锐角.证明x=y.
1.若cos x=5/13 及tan(x+y)= -120/119,其中x及y为锐角.证明x=y.
x为锐角
cos x=5/13 ,sinx=12/13
tanx=12/5
tan(x+y)
= (tanx+tany)/(1-tanx*tany)=-120/119
119*(12/5+tany)=120*12/5*tany-120
解得:tany=12/5
x及y为锐角,又tanx=tany
所以,x=y
1.若cos x=5/13 及tan(x+y)= -120/119,其中x及y为锐角.证明x=y.
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