已知sin(α+β)sin(α-β)=1/3.(1)求cos2β-cos2α的值;(2)求(1/4)(sin2α)^2+
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已知sin(α+β)sin(α-β)=1/3.(1)求cos2β-cos2α的值;(2)求(1/4)(sin2α)^2+(sinβ)^2+(cosα)^4
已知sin(α+β)sin(α-β)=1/3.(1)求cos2β-cos2α的值;(2)求(1/4)(sin2α)^2+(sinβ)^2+(cosα)^4的值.
(1)2/3;(2)2/3.
已知sin(α+β)sin(α-β)=1/3.(1)求cos2β-cos2α的值;(2)求(1/4)(sin2α)^2+(sinβ)^2+(cosα)^4的值.
(1)2/3;(2)2/3.
(1)因为sin(α+β)sin(α-β)=1/3
而cos2β-cos2α
=-2*sin(α+β)sin(β-α)
=2sin(α+β)sin(α-β)
=2/3
(2)(1/4)(sin2α)^2+(sinβ)^2+(cosα)^4
=1/4*(1-cos^2(2α))+(1-cos2β)/2+[(1+cos(2α))/2]^2
=1/4+(1-cos2β)/2+1/4+cos(2α)/2
=1/41/2+1/4-(cos2β-cos2α)/2
=1-1/3
=2/3
而cos2β-cos2α
=-2*sin(α+β)sin(β-α)
=2sin(α+β)sin(α-β)
=2/3
(2)(1/4)(sin2α)^2+(sinβ)^2+(cosα)^4
=1/4*(1-cos^2(2α))+(1-cos2β)/2+[(1+cos(2α))/2]^2
=1/4+(1-cos2β)/2+1/4+cos(2α)/2
=1/41/2+1/4-(cos2β-cos2α)/2
=1-1/3
=2/3
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