高1数学题5

求cos(A+15度)^2+cos(A-15度)^2-cos30度cos2A

热心网友

解：cos(A+15度)^2+cos(A-15度)^2-cos30度cos2A=[1+cos(2A+30度)]/2+[1+cos(2A-30度)]/2-cos30度cos2A=1+[cos(2A+30度)+cos(2A-30度)]/2-cos30度cos2A=1+cos(2A)cos30度-cos30度cos2A=1.

热心网友

cos(A+15度)^2+cos(A-15度)^2-cos30度cos2A=[1+cos(2A+30度)]/2+[1+cos(2A-30度)]/2-cos30度cos2A=1+[cos(2A+30度)+cos(2A-30度)]/2-cos30度cos2A=1+cos2Acos30度-cos30度cos2A=1.