Integral on WP 34s (and others)
02-21-2016, 10:11 PM
Post: #1
 lrdheat Senior Member Posts: 464 Joined: Feb 2014
Integral on WP 34s (and others)
When taking integral of (8x^2 + 26x + 15)/(2x^2 - x -15) from -5 to 0, I get out of domain error on the WP 34s. CASIO 9869gii and CLASSWIZ FX-991EX also fail. They all do fine if the lower start point is very close to -5 such as -5.0001. After fiddling around, I came to guess that this is due to denominator being undefined at X=-2.5, that one of the incremental dx' being added starts with -2.5

Is there an easy work around...

I was just about to submit, and realized that I could test this thought easily by adding 2 integrals where -2.5 would not likely be a starting point...I.e, integral from -5 to -3 plus integral from -3 to 0.

Works!

My ~62 year old mind isn't gone yet!
02-22-2016, 07:29 AM
Post: #2
 Dieter Senior Member Posts: 2,398 Joined: Dec 2013
RE: Integral on WP 34s (and others)
(02-21-2016 10:11 PM)lrdheat Wrote:  When taking integral of (8x^2 + 26x + 15)/(2x^2 - x -15) from -5 to 0, I get out of domain error on the WP 34s. CASIO 9869gii and CLASSWIZ FX-991EX also fail. They all do fine if the lower start point is very close to -5 such as -5.0001.

Sure. This way the (removable) singularity at x=–2,5 is (probably) not evaluated. This may happen with any integration method.

(02-21-2016 10:11 PM)lrdheat Wrote:  I was just about to submit, and realized that I could test this thought easily by adding 2 integrals where -2.5 would not likely be a starting point...I.e, integral from -5 to -3 plus integral from -3 to 0.

Another option: simplify the expression to (4x+3)/(x–3). Here the pole at x=3 is far beyond the integration limits. ;-)

Dieter
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