\(\displaystyle{\lim_{x\to \infty}}\sqrt{4x^2-x}-\sqrt{9x^2+1}+x\)
\(\displaystyle{\lim_{x\to \infty}}x\left(\sqrt{4-\frac 1 x}-\sqrt{3+\frac 1 x}+1\right)\)
\(\mbox{In the limit we can ignore the }\dfrac 1 x \mbox{ terms}\)
\(\displaystyle{\lim_{x\to \infty}}x\left(\sqrt{4}-\sqrt{3}+1\right)=\displaystyle{\lim_{x\to \infty}}x\left(3-\sqrt{3}\right)\)
\(3 > \sqrt{3} \mbox{ so } \\ \displaystyle{\lim_{x\to \infty}}x\left(3-\sqrt{3}\right)=+\infty \\ \mbox{and so } \\ \displaystyle{\lim_{x\to \infty}}\sqrt{4x^2-x}-\sqrt{9x^2+1}+x=+\infty\)
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