Nội dung mới nhất bởi THANHPHONGICT9X

tinh hinh la minh khong biet sai o dau nhung minh có cách khac. co gi thi mail nhe Cos^2x – ( cos(a+x) + cos(a-x))cos(a+x) + cos^2(a+x) = cos^2x – cos^2(a+x) – cos(a+x)cos(a-x) + cos^2(a+x) = cos^2x -1/2( cos2a + cos-2x) = cos^2x – 1/2cos2a –1/2(2cos^2x -1) = -1/2cos2a + ½ xong