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Mathematics 11 Online
OpenStudy (anonymous):

PLEASE HELP ME

OpenStudy (anonymous):

OpenStudy (anonymous):

I think A or B

OpenStudy (anonymous):

B or C*

jimthompson5910 (jim_thompson5910):

ignore the answer choices for a moment

jimthompson5910 (jim_thompson5910):

what does x^2 - 4 factor to?

OpenStudy (anonymous):

ok (x+2) (x-2)

jimthompson5910 (jim_thompson5910):

correct

jimthompson5910 (jim_thompson5910):

so what we do is factor the denominator and you'll see a pair of terms cancel

jimthompson5910 (jim_thompson5910):

\[\Large \frac{-5}{5x+15} \cdot \frac{2(x+2)}{x^2-4}\] \[\Large \frac{-5}{5x+15} \cdot \frac{2(x+2)}{(x+2)(x-2)}\] \[\Large \frac{-5}{5x+15} \cdot \frac{2\cancel{(x+2)}}{\cancel{(x+2)}(x-2)}\] \[\Large \frac{-5}{5x+15} \cdot \frac{2}{x-2}\]

jimthompson5910 (jim_thompson5910):

making sense so far?

OpenStudy (anonymous):

yes

jimthompson5910 (jim_thompson5910):

now, what does 5x+15 factor to?

OpenStudy (anonymous):

can I tell you what I think it is I tried doing the math

jimthompson5910 (jim_thompson5910):

what do you think 5x+15 factors to

OpenStudy (anonymous):

5x + 15

jimthompson5910 (jim_thompson5910):

try factoring out the GCF

OpenStudy (anonymous):

one sec

OpenStudy (anonymous):

5(x+3)

jimthompson5910 (jim_thompson5910):

yep

OpenStudy (anonymous):

:)

jimthompson5910 (jim_thompson5910):

\[\Large \frac{-5}{5x+15} \cdot \frac{2}{x-2}\] \[\Large \frac{-5}{5(x+3)} \cdot \frac{2}{x-2}\] \[\Large \frac{-\cancel{5}}{\cancel{5}(x+3)} \cdot \frac{2}{x-2}\] \[\Large \frac{-1}{x+3} \cdot \frac{2}{x-2}\]

jimthompson5910 (jim_thompson5910):

then you multiply the fractions (straight across: numerator with numerator, denominator with denominator) \[\Large \frac{-1}{x+3} \cdot \frac{2}{x-2}\] \[\Large \frac{-1*2}{(x+3)(x-2)}\] \[\Large \frac{-2}{(x+3)(x-2)}\]

jimthompson5910 (jim_thompson5910):

so \[\Large \frac{-5}{5x+15} \cdot \frac{2(x+2)}{x^2-4}\] simplifies to \[\Large \frac{-2}{(x+3)(x-2)}\]

jimthompson5910 (jim_thompson5910):

the question is now: what is the domain?

jimthompson5910 (jim_thompson5910):

to answer that sub-question, you need to set every denominator in the original expression equal to zero and solve

jimthompson5910 (jim_thompson5910):

5x+15 = 0 ----> x = ??? x^2 - 4 = 0 ----> x = ???

OpenStudy (anonymous):

its C thank you !

jimthompson5910 (jim_thompson5910):

yep, correct

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