# Limits with Square roots Question help

by Sleighty
Tags: calculus, cos x, limit, limits, square roots
 Math Emeritus Sci Advisor Thanks PF Gold P: 39,568 You are completely wrong about this problem- you cannot use the "addition/subtraction" law here because you cannot add/subtract "infinity". Think of this as the fraction $$\frac{\sqrt{x^2+ 4x}- x(cos(x))}{1}$$ and "rationalize the numerator"- multiply numerator and denominator by $$\sqrt{x^2+ 4x(cos(x)}+ x$$.
 Math Emeritus Sci Advisor Thanks PF Gold P: 39,568 Limits with Square roots Question help Sorry I accidently dropped it. I have edited my previous posts: Multiply numerator and denominator by $$\sqrt{x^2+ 4x(cos(x)}+ x$$.