cos2x - cos3x = 2 sin(5x/2) sin(x/2)
原式= lim(x->0) 2 sin(5x/2) sin(x/2) / x² 等价无穷小代换 sin(5x/2) 5x/2 sin(x/2) x/2
= lim(x->0) 2 (5x/2) (x/2) / x²
= 5/2
cos2x - cos3x = 2 sin(5x/2) sin(x/2)
原式= lim(x->0) 2 sin(5x/2) sin(x/2) / x² 等价无穷小代换 sin(5x/2) 5x/2 sin(x/2) x/2
= lim(x->0) 2 (5x/2) (x/2) / x²
= 5/2