Khan/khan-exercises — Issue #6518: Limits 2 - Limit question has the wrong answer
Author: KhanBugz
Created: 2011-11-17 09:13:25+00:00
State: open
Labels: firefox, win7, wrong-or-unclear

Graphing the equation as well as checking the math with approaching numbers shows the answer to be negative infinity. Copy/paste of the hint text as well as the question:
Find limx→−1−7x+1.

Consider the behavior of the function as x→−1 from each direction.

As x approaches −1 from the left, x+1 starts negative and increases as it approaches 0, so −7x+1 approaches −∞.

As x approaches −1 from the right, x+1 starts positive and decreases as it approaches 0, so −7x+1 approaches +∞.

Since the left- and right-hand limits are not equal, the limit is not defined.

-----------------------------
Here is where I believe the error is:
As x approaches −1 from the right, x+1 starts positive and decreases as it approaches 0, so −7x+1 approaches +∞.

[limits_2.html?seed=149&problem=a-o-xmk](http://sandcastle.khanacademy.org/media/castles/Khan:master/exercises/limits_2.html?seed=149&problem=a-o-xmk&debug)

[Answer timeline](http://sandcastle.khanacademy.org/media/castles/Khan:master/exercises/limits_2.html?seed=149&problem=a-o-xmk&debug&activity=%5B%5B%22incorrect-activity%22%2C%22%5C%22%3Ccode%20style%3D%5C%5C%5C%22display%3A%20none%3B%5C%5C%5C%22%3E-%5C%5C%5C%5Cinfty%3C%2Fcode%3E%5C%22%22%2C75%5D%2C%5B%22hint-activity%22%2C%220%22%2C65%5D%2C%5B%22hint-activity%22%2C%220%22%2C70%5D%2C%5B%22hint-activity%22%2C%220%22%2C80%5D%2C%5B%22hint-activity%22%2C%220%22%2C169%5D%5D)

["-\\infty"]

Mozilla/5.0 (Windows NT 6.1; rv:8.0) Gecko/20100101 Firefox/8.0

MathJax is loaded, ready, queue length: 0