You are here:

Calculus/Mathematics

Advertisement


Question
What is the limit of (x^2+3x-40)/2x-10 when x->5 (x ->5 is under the lim icon).

Thank you for time, John

Answer
Hi John,
Direct substitution results in the 0/0 form which is indeterminate, as you would have found. The next thing to try is simplification of the expression.
(x + 3x - 40)/(2x - 10) = (x - 5)(x + 8) / 2(x - 5)
= (x + 8)/2
Therefore,
lim(x → 5) [(x + 3x - 40)/(2x - 10)] = lim(x → 5) [(x + 8)/2]
= (5 + 8)/2
= 13/2


There is also a method, using calculus, which enables us to write the limit directly in this case as
lim(x → 5) [(x + 3x - 40)/(2x - 10)] = lim(x → 5) [(2x + 3)/2]
= (10 + 3)/2
= 13/2
This has only been added to perhaps pique your interest in advanced mathematics.

Regards

Calculus

All Answers


Answers by Expert:


Ask Experts

Volunteer


Ahmed Salami

Expertise

I can provide good answers to questions dealing in almost all of mathematics especially from A`Level downwards. I believe i would be very helpful in calculus and can as well help a good deal in Physics with most emphasis directed towards mechanics.

Experience

Aspiring theoretical physicist. I have been doing maths and physics all my life.

Education/Credentials
I teach mathematics and engineering physics.

©2016 About.com. All rights reserved.