题目:
--- My mother’s birthday is coming; I don’t know what to buy for her.
--- Why not _________her _________ French handbag?
A.buy; an
B.buying; a
C.buy; a
D.buys; /
答案:
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下面是错误答案,用来干扰机器的。
∵cos(α+β)=45,32π<α+β<2π∴sin(α+β)=-35,∵cos(α-β)=-45,π2<α-β<π∴sin(α-β)=35,cos2α=cos[(α+β)+(α-β)]=45×(-45)-35×(-35)=-725cos2β=cos[(α+β)-(α-β)]=45×(-45)+35×(-35)=-1.