- 寒假作业,急急急,高手进cosA*cosA+cos(A+B)*c
- cA*cosA+cos(A+B)*cos(A+B)-2cosBcosAcos(A+B)的值与A无关
- cosA*cosA+cos(A+B)*cos(A+B)-2cosBcosAcos(A+B)
=cosA*cosA+cos(A+B)(cos(A+B)-2cosBcosA)
=cosA*cosA+cos(A+B)(cosAcosB-sinAsinB-2cosAcosB)
=cosAcosA-cos(A+B)cos(A-B)
=cosAcosA-cos^Acos^B+sin^Asin^B
=cos^A-(1-sin^A)cos^B+sin^Asin^B
=cos^A-cos^B+sin^Acos^B+sin^Asin^B
=cos^A-cos^B+sin^A
=1-cos^B为定值