: 1.lim √(x^2+2x)－x =
: x→∞
√(x^2+2x) - x = x√[1+(2/x)] - x = x[1+(1/x)-(1/2x^2)...] - x = 1 - 1/2x +...
lim √(x^2+2x) - x = 1
x→∞
: 2. sin(3x)*cos(2x)
: lim ──────── =
: x→∞ tan(6x)
mathematica: 不存在
: 3.a line pass through (0,0) is tangent to y=x^3+3x+1 上的(a,b) 求a
dy b