cosa cosb = [ cos(a+b) + cos(a-b) ] / 2
y=cosxcos2x
= [ cos 3x + cos x ] / 2
= [ cos 3x ] / 2 + [ cos x ] / 2
cos kxçné¶å¯¼æ° = k^n cos(kx+nÏ/2)
代è¿å»ä¹å
yçné¶å¯¼æ°ä¸º[3^n cos (3x+nÏ/2) ] / 2 + [ cos (x+nÏ/2) ] / 2
温馨提示:答案为网友推荐,仅供参考