大一微积分,求下列各极限,

大一微积分,求下列各极限,1x→+∞ x^n/e^2x2x→π/2 tan3x/tanx3x→0 (1/x-1/tanx)4x→∞ (x+e^x)^1/x5x→1 (1/1-x^3-1/1-x)6x→0+ (cosx)^1/x