Mathematics
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OpenStudy (anonymous):
PLEASE HELP ME
11 years ago
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OpenStudy (anonymous):
11 years ago
OpenStudy (anonymous):
I think A or B
11 years ago
OpenStudy (anonymous):
B or C*
11 years ago
jimthompson5910 (jim_thompson5910):
ignore the answer choices for a moment
11 years ago
jimthompson5910 (jim_thompson5910):
what does x^2 - 4 factor to?
11 years ago
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OpenStudy (anonymous):
ok (x+2) (x-2)
11 years ago
jimthompson5910 (jim_thompson5910):
correct
11 years ago
jimthompson5910 (jim_thompson5910):
so what we do is factor the denominator and you'll see a pair of terms cancel
11 years ago
jimthompson5910 (jim_thompson5910):
\[\Large \frac{-5}{5x+15} \cdot \frac{2(x+2)}{x^2-4}\]
\[\Large \frac{-5}{5x+15} \cdot \frac{2(x+2)}{(x+2)(x-2)}\]
\[\Large \frac{-5}{5x+15} \cdot \frac{2\cancel{(x+2)}}{\cancel{(x+2)}(x-2)}\]
\[\Large \frac{-5}{5x+15} \cdot \frac{2}{x-2}\]
11 years ago
jimthompson5910 (jim_thompson5910):
making sense so far?
11 years ago
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OpenStudy (anonymous):
yes
11 years ago
jimthompson5910 (jim_thompson5910):
now, what does 5x+15 factor to?
11 years ago
OpenStudy (anonymous):
can I tell you what I think it is I tried doing the math
11 years ago
jimthompson5910 (jim_thompson5910):
what do you think 5x+15 factors to
11 years ago
OpenStudy (anonymous):
5x + 15
11 years ago
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jimthompson5910 (jim_thompson5910):
try factoring out the GCF
11 years ago
OpenStudy (anonymous):
one sec
11 years ago
OpenStudy (anonymous):
5(x+3)
11 years ago
jimthompson5910 (jim_thompson5910):
yep
11 years ago
OpenStudy (anonymous):
:)
11 years ago
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jimthompson5910 (jim_thompson5910):
\[\Large \frac{-5}{5x+15} \cdot \frac{2}{x-2}\]
\[\Large \frac{-5}{5(x+3)} \cdot \frac{2}{x-2}\]
\[\Large \frac{-\cancel{5}}{\cancel{5}(x+3)} \cdot \frac{2}{x-2}\]
\[\Large \frac{-1}{x+3} \cdot \frac{2}{x-2}\]
11 years ago
jimthompson5910 (jim_thompson5910):
then you multiply the fractions (straight across: numerator with numerator, denominator with denominator)
\[\Large \frac{-1}{x+3} \cdot \frac{2}{x-2}\]
\[\Large \frac{-1*2}{(x+3)(x-2)}\]
\[\Large \frac{-2}{(x+3)(x-2)}\]
11 years ago
jimthompson5910 (jim_thompson5910):
so
\[\Large \frac{-5}{5x+15} \cdot \frac{2(x+2)}{x^2-4}\]
simplifies to
\[\Large \frac{-2}{(x+3)(x-2)}\]
11 years ago
jimthompson5910 (jim_thompson5910):
the question is now: what is the domain?
11 years ago
jimthompson5910 (jim_thompson5910):
to answer that sub-question, you need to set every denominator in the original expression equal to zero and solve
11 years ago
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jimthompson5910 (jim_thompson5910):
5x+15 = 0 ----> x = ???
x^2 - 4 = 0 ----> x = ???
11 years ago
OpenStudy (anonymous):
its C thank you !
11 years ago
jimthompson5910 (jim_thompson5910):
yep, correct
11 years ago