问题
解答题
已知tgx=a，求
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答案
=3sinx+sin3x 3cosx+cos3x
=2sinx+sinx+sin3x 2cosx+cosx+cos3x 2sinx+2sin2xcosx 2cosx+2cos2xcosx
=
=2sinx+4sinxcos2x 2cosx(1+cos2x)
=tgx(1+2cos2x) 2cos2x
(sec2x+2)=tgx 2
(tg2x+3)tgx 2
=
(a2+3)a 2