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问题: 一道数学题

如图.

解答:

解:[sin(2π-α)tan(π+α)cos(π/2-α)]/[cos(π-α)tan(3π-α)tan(-α-π)]=[-sinα*tanα*sinα]/[-cosα(-tanα)(-tan(α+π)]
=[-sinαtanαsinα]/[cosαtanα(-tanα)]
=sinαsinα/cosαtanα=sinα