已知sin a+cos a= -1/5 求1）sin acos a 2）sin a-cos a
人气：456 ℃ 时间：2020-03-28 22:26:28
解答
sin a+cos a= -1/5 平方(sin a+cos a)^2= 1/25 (sin a)^2+2sin acos a+(cos a)^2= 1/25 1+2sin acos a= 1/25 2sin acos a= -24/25 sin acos a= -12/25 (sin a-cos a)^2=(sin a)^2-2sin acos a+(cos a)^2=1-2sin acos...
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