已知角α的终边过点P(4/5,-3/5).(1)求sinα的值.(2)求式子sin(π/2-α)/sin(α+π)*tan(α-π)/cos(3π-α)的值.

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已知角α的终边过点P(4/5,-3/5).(1)求sinα的值.(2)求式子sin(π/2-α)/sin(α+π)*tan(α-π)/cos(3π-α)的值.

已知角α的终边过点P(4/5,-3/5).(1)求sinα的值.(2)求式子sin(π/2-α)/sin(α+π)*tan(α-π)/cos(3π-α)的值.
已知角α的终边过点P(4/5,-3/5).(1)求sinα的值.
(2)求式子sin(π/2-α)/sin(α+π)*tan(α-π)/cos(3π-α)的值.

已知角α的终边过点P(4/5,-3/5).(1)求sinα的值.(2)求式子sin(π/2-α)/sin(α+π)*tan(α-π)/cos(3π-α)的值.
即sinα=3/5 /((4/5)²+(3/5)²)½=3/5
sin(π/2-α)/sin(α+π)*tan(α-π)/cos(3π-α)= cosα/(-sin α)*(-tan(π-α)/cosα)=-1/tanα*tanα/cosα
=-1/cosα
((4/5)²+(3/5)²)½=1,
-1/cosα=-1/((4/5)/1)=-5/4