'Misconception' regrading multiplication of zero by infinity

The 'Common Misconception' section of Calculus states that the multiplication of zero by infinity does not give zero. And it is followed by example of multiplying g(x) and h(x) where g(x) = x as x tends to 0 and h(x) =1/x as x tends to 0.

My problem with this explanation that here g(x) is not EXACTLY equal to 0. If we take g(x) = 0 (instead of tending to zero), and h(x) be same as before (that is, 1/x where x tends to 0), won't g(x)×h(x) give zero?

#Calculus

Easy Math Editor

This discussion board is a place to discuss our Daily Challenges and the math and science related to those challenges. Explanations are more than just a solution — they should explain the steps and thinking strategies that you used to obtain the solution. Comments should further the discussion of math and science.

When posting on Brilliant:

Use the emojis to react to an explanation, whether you're congratulating a job well done , or just really confused .
Ask specific questions about the challenge or the steps in somebody's explanation. Well-posed questions can add a lot to the discussion, but posting "I don't understand!" doesn't help anyone.
Try to contribute something new to the discussion, whether it is an extension, generalization or other idea related to the challenge.
Stay on topic — we're all here to learn more about math and science, not to hear about your favorite get-rich-quick scheme or current world events.

Markdown	Appears as
`italics` or `_italics_`	italics
`bold` or `__bold__`	bold
- bulleted - list	bulleted list
1. numbered 2. list	numbered list
Note: you must add a full line of space before and after lists for them to show up correctly
paragraph 1 paragraph 2	paragraph 1 paragraph 2
`[example link](https://brilliant.org)`	example link
`> This is a quote`	This is a quote
# I indented these lines # 4 spaces, and now they show # up as a code block. print "hello world"	# I indented these lines # 4 spaces, and now they show # up as a code block. print "hello world"

Math	Appears as
Remember to wrap math in `$` ... `$` or `\[` ... `\]` to ensure proper formatting.
`2 \times 3`	$2 \times 3$
`2^{34}`	$2^{34}$
`a_{i-1}`	$a_{i-1}$
`\frac{2}{3}`	$\frac{2}{3}$
`\sqrt{2}`	$\sqrt{2}$
`\sum_{i=1}^3`	$\sum_{i=1}^3$
`\sin \theta`	$\sin \theta$
`\boxed{123}`	$\boxed{123}$

Comments

At $x=0$ , $g(x)$ is equal to 0, but $h(x)$ is undefined. You can't perform arithmetic operation on undefined.

Pi Han Goh - 1 year, 10 months ago

I had made a mistake while defining h(x). Now I have changed the definition of h(x) so that h(x) is a very large positive number (that is, infinity), and hence not undefined.

So now if we multiply g(x) and h(x), won't the result be zero?

Aumkaar Shukla - 1 year, 10 months ago

To clarify: Infinity is not a number, it is just a concept.

Pi Han Goh - 1 year, 10 months ago

Math	Appears as
Remember to wrap math in `\(` ... `\)` or `\[` ... `\]` to ensure proper formatting.
`2 \times 3`	$2 \times 3$
`2^{34}`	$2^{34}$
`a_{i-1}`	$a_{i-1}$
`\frac{2}{3}`	$\frac{2}{3}$
`\sqrt{2}`	$\sqrt{2}$
`\sum_{i=1}^3`	$\sum_{i=1}^3$
`\sin \theta`	$\sin \theta$
`\boxed{123}`	$\boxed{123}$