sina+cosa=1/5
两边同时平方得:
sin²a+2sinacosa+cos²a=1/25
1+2sinacosa=1/25
2sinacosa=-24/25
sinacosa=-12/25
(cosa-sina)²
=sin²a-2sinacosa+cos²a
=1-2sinacosa
=1-(-24/25)
=1+24/25
=49/25
故cosa-sina=±7/5
因为sinacosa=-12/25<0
0<a<π
所以cosa<0,sina>0
故cosa-sina
已知sina+cosa=1/5,0
已知sina+cosa=1/5,0
数学人气:828 ℃时间:2020-03-18 10:04:38
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