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What is the sum?

[tex]\[ \frac{3}{x^2-9} + \frac{5}{x+3} \][/tex]

A. \(\frac{8}{x^2+x-6}\)

B. \(\frac{5x-12}{x-3}\)

C. \(\frac{-5x}{(x+3)(x-3)}\)

D. [tex]\(\frac{5x-12}{(x+3)(x-3)}\)[/tex]

Sagot :

Certainly! Let's find the sum of the given fractions step-by-step.

We are given these expressions:
[tex]\[ \frac{3}{x^2-9} + \frac{5}{x+3} + \frac{8}{x^2+x-6} + \frac{5x - 12}{x-3} + \frac{-5x}{(x+3)(x-3)} + \frac{5x-12}{(x+3)(x-3)} \][/tex]

First, we need to factorize the denominators whenever possible:

1. \(x^2 - 9 = (x-3)(x+3)\)
2. \(x^2 + x - 6 = (x-3)(x+3)\)

Substituting these factorizations back into the fractions:

[tex]\[ \frac{3}{(x-3)(x+3)} + \frac{5}{x+3} + \frac{8}{(x-3)(x+3)} + \frac{5x - 12}{x-3} + \frac{-5x}{(x+3)(x-3)} + \frac{5x - 12}{(x+3)(x-3)} \][/tex]

Now, let's align all fractions to have a common denominator, which is \((x-3)(x+3)\):

[tex]\[ \frac{3 + 8 - 5x + 5x - 12}{(x-3)(x+3)} + \frac{5(x-3)}{(x-3)(x+3)} + \frac{5(-3)}{(x-3)(x+3)} \][/tex]

Combine the numerators accordingly:

[tex]\[ \frac{3 + 8 + (5x-12) - 5x}{(x-3)(x+3)} + \frac{5(x-3)}{(x-3)(x+3)} \][/tex]

Notice that combining \((5x-12) - 5x\) would yield:

[tex]\[ 5x - 12 - 5x = -12 \][/tex]

Thus simplifying further:

[tex]\[ \frac{3 + 8 - 12}{(x-3)(x+3)} + \frac{5(x-3)}{(x-3)(x+3)} \][/tex]

This further simplifies by combining like terms:

[tex]\[ \frac{-1 + 5(x-3)}{(x-3)(x+3)} \][/tex]

Distribute 5 in the numerator:

[tex]\[ \frac{-1 + 5x - 15}{(x-3)(x+3)} \][/tex]

Combine:

[tex]\[ \frac{5x - 16}{(x-3)(x+3)} \][/tex]

Putting it all together, the sum of these fractions simplifies to:

[tex]\[ \frac{5x^3 - 2x^2 - 68x + 96}{x^3 - 2x^2 - 9x + 18} \][/tex]

This final form is fully simplified and cannot be reduced further. Thus, the sum of the given fractions is:

[tex]\[ \frac{5x^3 - 2x^2 - 68x + 96}{x^3 - 2x^2 - 9x + 18} \][/tex]