(sina+sinb)^2+(cosa+cosb)^2=?A.(COS(a-b)/2)^2B.4(COS(a-b)/2)^2C.._数学解答

(sina+sinb)^2+(cosa+cosb)^2=?
A.(COS(a-b)/2)^2
B.4(COS(a-b)/2)^2
C..(sin(a-b)/2)^2

人气：491 ℃　时间：2020-02-26 02:36:24

解答

(sina+sinb)^2+(cosa+cosb)^2
=sin²a+2sina*sinb+sin²b+cos²a+2cosa*cosb+cos²b
=2+2(sina*sinb+cosa*cosb)
=2+2cos(a-b)