已知3sin(-5∏-A)=4cos(A-6∏),求2sin^2A+sinA*cosA-3cos^2A之值?急,
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![已知3sin(-5∏-A)=4cos(A-6∏),求2sin^2A+sinA*cosA-3cos^2A之值?急,](/uploads/image/z/2758201-25-1.jpg?t=%E5%B7%B2%E7%9F%A53sin%28-5%E2%88%8F-A%29%3D4cos%28A-6%E2%88%8F%29%2C%E6%B1%822sin%5E2A%2BsinA%2AcosA-3cos%5E2A%E4%B9%8B%E5%80%BC%3F%E6%80%A5%2C)
已知3sin(-5∏-A)=4cos(A-6∏),求2sin^2A+sinA*cosA-3cos^2A之值?急,
已知3sin(-5∏-A)=4cos(A-6∏),求2sin^2A+sinA*cosA-3cos^2A之值?急,
已知3sin(-5∏-A)=4cos(A-6∏),求2sin^2A+sinA*cosA-3cos^2A之值?急,
∵3sin(-5π-A)=4cos(A-6π)
∴3sinA=4cosA
∴tana=4/3
∵2sin^2A+sinA*cosA-3cos^2A
=(2sin^2A+sinA*cosA-3cos^2A)/(sin^2A+cos^2A)
=(2tan^2A+tanA-3)/(tan^2A+1)
=(2×16/9+4/3-3)/(16/9+1)
=17/25