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What is the solution of [tex]\frac{-8}{2y-8}=\frac{5}{y+4}-\frac{7y+8}{y^2-16}[/tex]?

A. [tex]y=-4[/tex]
B. [tex]y=-2[/tex]
C. [tex]y=4[/tex]
D. [tex]y=6[/tex]

Sagot :

To solve the equation [tex]\(\frac{-8}{2 y-8}=\frac{5}{y+4}-\frac{7 y+8}{y^2-16}\)[/tex], let's go through it step-by-step.

First, simplify and rewrite the terms wherever possible:

1. Recall that:
[tex]\[ y^2 - 16 = (y - 4)(y + 4) \][/tex]

2. Rewrite the original equation:
[tex]\[ \frac{-8}{2 y-8}=\frac{5}{y+4}-\frac{7 y+8}{(y-4)(y+4)} \][/tex]

3. Simplify the first fraction on the left-hand side:
[tex]\[ 2y - 8 = 2(y - 4) \implies \frac{-8}{2(y-4)} = \frac{-4}{y-4} \][/tex]
So, the equation becomes:
[tex]\[ \frac{-4}{y-4} = \frac{5}{y+4} - \frac{7y+8}{(y-4)(y+4)} \][/tex]

4. To have a common denominator, combine the right-hand side terms under a single denominator:
[tex]\[ \frac{5}{y+4} - \frac{7y + 8}{(y-4)(y+4)} \][/tex]

5. Express each fraction with the common denominator [tex]\((y-4)(y+4)\)[/tex]:
[tex]\[ \frac{5(y-4)}{(y-4)(y+4)} - \frac{7y+8}{(y-4)(y+4)} \][/tex]

6. Combine the fractions:
[tex]\[ \frac{5(y-4) - (7y+8)}{(y-4)(y+4)} \][/tex]

7. Simplify the numerator:
[tex]\[ 5(y-4) = 5y - 20 \][/tex]
[tex]\[ 5(y-4) - (7y+8) = 5y - 20 - 7y - 8 = -2y - 28 \][/tex]

8. This gives:
[tex]\[ \frac{-2y - 28}{(y-4)(y+4)} \][/tex]

So, the equation now looks like:
[tex]\[ \frac{-4}{y-4} = \frac{-2y - 28}{(y-4)(y+4)} \][/tex]

9. Cross-multiply to eliminate the fractions:
[tex]\[ -4(y+4) = (-2y-28) \][/tex]

10. Simplify:
[tex]\[ -4y - 16 = -2y - 28 \][/tex]

11. Bring like terms together:
[tex]\[ -4y + 2y = -28 + 16 \][/tex]
[tex]\[ -2y = -12 \][/tex]

12. Solve for [tex]\( y \)[/tex]:
[tex]\[ y = 6 \][/tex]

Therefore, the solution to the equation is:
[tex]\[ y = 6 \][/tex]