In calculus, the limit of x/x as x approaches infinity is 1. However, by the product rule, it would be the limit of x * limit of 1/x, which in turn evaluates to 0. Why is this so, and which one is wrong?

Respuesta :

Answer:

[tex]\lim_{x \to \infty} \frac{x}{x}=1[/tex]

Calculating the limit by product rule is WRONG

Step-by-step explanation:

Indeterminate Forms:

Indeterminate forms is an expression involving 2 functions whose limit cannot be determined by limits of individual functions. If we calculate the limits by general rules used for calculating the limits, we will not have a clear answer.

Examples of indeterminate forms are:

[tex]\frac{0}{0}, \frac{\infty}{\infty} , 0\cdot\infty, 1^{\infty},\infty-\infty, 0^0,\infty^0[/tex]

To find the limits of such forms, we have to use L'hospital rule, which states that if:

[tex]\lim_{x \to \infty} \frac{f(x)}{g(x)} = Indeterminate form \\ Then\\\lim_{x \to \infty} \frac{f(x)}{g(x)} = \lim_{x \to \infty} \frac{f'(x)}{g'(x)}[/tex]

Solve the question:

[tex]\lim_{x \to \infty} \frac{x}{x}= \lim_{x \to \infty} x\cdot \lim_{x \to \infty} \frac{1}{x} \\ \lim_{x \to \infty} \frac{x}{x}= =\infty\cdot\frac{1}{\infty} \\ \lim_{x \to \infty} \frac{x}{x}=\infty\cdot0[/tex]

As it is an INDETERMINATE FORM, we cannot calculate its limit by product rule. We have to use L'Hospital Rule:

[tex]\lim_{x \to \infty} \frac{x}{x}= \lim_{x \to \infty} \frac{d(x)/dx}{d(x)/dx}\\\lim_{x \to \infty} \frac{x}{x}=\lim_{x \to \infty} \frac{1}{1}\\\lim_{x \to \infty} \frac{x}{x}=1[/tex]