已知tan a=2,求(1)(sin a-3cos a)/(sin a+cos a) (2)(2sin^2 a-3cos^2 a)/(4sin^2 a-9cos^2 a)(3)4sin^2 a-3cos axsin a-5cos^ a
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![已知tan a=2,求(1)(sin a-3cos a)/(sin a+cos a) (2)(2sin^2 a-3cos^2 a)/(4sin^2 a-9cos^2 a)(3)4sin^2 a-3cos axsin a-5cos^ a](/uploads/image/z/2095232-32-2.jpg?t=%E5%B7%B2%E7%9F%A5tan+a%3D2%2C%E6%B1%82%281%29%28sin+a-3cos+a%29%2F%28sin+a%2Bcos+a%29+%282%29%282sin%5E2+a-3cos%5E2+a%29%2F%284sin%5E2+a-9cos%5E2+a%29%283%294sin%5E2+a-3cos+axsin+a-5cos%5E+a)
已知tan a=2,求(1)(sin a-3cos a)/(sin a+cos a) (2)(2sin^2 a-3cos^2 a)/(4sin^2 a-9cos^2 a)(3)4sin^2 a-3cos axsin a-5cos^ a
已知tan a=2,求(1)(sin a-3cos a)/(sin a+cos a) (2)(2sin^2 a-3cos^2 a)/(4sin^2 a-9cos^2 a)
(3)4sin^2 a-3cos axsin a-5cos^ a
已知tan a=2,求(1)(sin a-3cos a)/(sin a+cos a) (2)(2sin^2 a-3cos^2 a)/(4sin^2 a-9cos^2 a)(3)4sin^2 a-3cos axsin a-5cos^ a
(1)(sin a-3cos a)/(sin a+cos a)
=(tana-3)/(tana+1)
=-2/3
(2)(2sin^2 a-3cos^2 a)/(4sin^2 a-9cos^2 a)
=[2(tana)^2-3]/[(4(tana)^2-9]
=1/7
(3)本题问题错误.
(1)分子分母同时除以cos a,得出结果为-1/3。
(2)分子分母同时除以cos^2 a,得出结果为5/7。
(3)将其除以sin^2 a+cos^2 a,然后再分子分母同除以cos^2 a,得出结果为1。.