已知sin(a+B)sin(a-B)=1/3,求cos2b-cos2a_数学解答

已知sin(a+B)sin(a-B)=1/3,求cos2b-cos2a

人气：229 ℃　时间：2020-07-04 06:57:36

解答

cos2b-cos2a
=cos[(a+b)-(a-b)]-cos[(a+b)+(a-b)]
=[cos(a+b)cos(a-b)+sin(a+b)sin(a-b)]-
[cos(a+b)cos(a-b)-sin(a+b)sin(a-b)]
=2sin(a+b)sin(a-b)
=2/3