已知tana=2,求3\4sin^2a+1\2+sin2a
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已知tana=2,求3\4sin^2a+1\2+sin2a
写错了,是3\4sin^2a+1\2+sin2a
写错了,是3\4sin^2a+1\2+sin2a
3/(4sin^2a+1\2+sin2a)
=3(sin^2a+cos^2a)/(4sin^2a+sin^2a+cos^2a\2+2sinacosa)
=3(sin^2a+cos^2a)/(5sin^2a+cos^2a\2+2sinacosa)分子分母同时除以cos^2a
=3(sin^2a/cos^2a+cos^2a/cos^2a)/(5sin^2a/cos^2a+cos^2a/cos^2a\2+2sinacosa/cos^2a)
=3(tan^2a+1)/(5tan^2a+1\2+2tana)
=3*(2^2+1)/(5*2^2+1\2+2*2)
=15/25
=3/5
再问: 写错了,是3\4sin^2a+1\2+sin2a
=3(sin^2a+cos^2a)/(4sin^2a+sin^2a+cos^2a\2+2sinacosa)
=3(sin^2a+cos^2a)/(5sin^2a+cos^2a\2+2sinacosa)分子分母同时除以cos^2a
=3(sin^2a/cos^2a+cos^2a/cos^2a)/(5sin^2a/cos^2a+cos^2a/cos^2a\2+2sinacosa/cos^2a)
=3(tan^2a+1)/(5tan^2a+1\2+2tana)
=3*(2^2+1)/(5*2^2+1\2+2*2)
=15/25
=3/5
再问: 写错了,是3\4sin^2a+1\2+sin2a
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