sin110sin20/((cos155)^2-(sin155)^2) 等于多少,有图且正确必采纳
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sin110sin20/((cos155)^2-(sin155)^2)
=sin(180-70)sin20/cos(155x2)
=sin70sin20/cos310
=sin70sin20/cos(360-50)
=sin70sin20/cos50
=sin(90-20)sin20/cos50
=cos20sin20/cos50
=2cos20sin20/2cos50
=sin40/2cos50
=sin(90-50)/2cos50
=cos50/2cos50
=1/2
=sin(180-70)sin20/cos(155x2)
=sin70sin20/cos310
=sin70sin20/cos(360-50)
=sin70sin20/cos50
=sin(90-20)sin20/cos50
=cos20sin20/cos50
=2cos20sin20/2cos50
=sin40/2cos50
=sin(90-50)/2cos50
=cos50/2cos50
=1/2
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