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Determine the values of [tex]\( A \)[/tex] and [tex]\( B \)[/tex] for the partial fraction decomposition form of [tex]\(\frac{x}{x^2 - 5x + 6}\)[/tex]:

A. [tex]\( 4, 5 \)[/tex]
B. [tex]\( -2, 3 \)[/tex]
C. [tex]\( 2, 3 \)[/tex]
D. [tex]\( 2, -3 \)[/tex]

Sagot :

To solve for the values of [tex]\( A \)[/tex] and [tex]\( B \)[/tex] for the partial fraction decomposition of the given function, we follow these steps:

1. Given Expression: We start with the fraction:
[tex]\[ \frac{x}{x^2 - 5x + 6} \][/tex]

2. Factor the Denominator: The denominator [tex]\( x^2 - 5x + 6 \)[/tex] factors into:
[tex]\[ x^2 - 5x + 6 = (x - 2)(x - 3) \][/tex]

3. Set up the Partial Fractions: We express the fraction as a sum of partial fractions with unknown coefficients [tex]\( A \)[/tex] and [tex]\( B \)[/tex]:
[tex]\[ \frac{x}{(x-2)(x-3)} = \frac{A}{x-2} + \frac{B}{x-3} \][/tex]

4. Combine the Fractions on the Right-Hand Side: To combine the fractions, we write:
[tex]\[ \frac{A}{x-2} + \frac{B}{x-3} = \frac{A(x-3) + B(x-2)}{(x-2)(x-3)} \][/tex]

5. Set the Numerators Equal: Since the denominators are the same, we can equate the numerators:
[tex]\[ x = A(x-3) + B(x-2) \][/tex]

6. Expand the Right-Hand Side: Distribute [tex]\( A \)[/tex] and [tex]\( B \)[/tex]:
[tex]\[ x = Ax - 3A + Bx - 2B \][/tex]

7. Combine Like Terms: Combine the terms involving [tex]\( x \)[/tex]:
[tex]\[ x = (A + B)x - 3A - 2B \][/tex]

8. Set up a System of Equations: For the equation [tex]\( x = (A + B)x - 3A - 2B \)[/tex] to hold for all [tex]\( x \)[/tex], the coefficients on both sides must be equal. This gives us two simultaneous equations:
[tex]\[ A + B = 1 \][/tex]
[tex]\[ -3A - 2B = 0 \][/tex]

9. Solve the System of Equations:
- From the first equation, solve for [tex]\( A \)[/tex]:
[tex]\[ A = 1 - B \][/tex]
- Substitute [tex]\( A = 1 - B \)[/tex] into the second equation:
[tex]\[ -3(1 - B) - 2B = 0 \][/tex]
- Simplify and solve for [tex]\( B \)[/tex]:
[tex]\[ -3 + 3B - 2B = 0 \][/tex]
[tex]\[ 3B - 2B = 3 \][/tex]
[tex]\[ B = 3 \][/tex]
- Substitute [tex]\( B = 3 \)[/tex] back into [tex]\( A = 1 - B \)[/tex]:
[tex]\[ A = 1 - 3 \][/tex]
[tex]\[ A = -2 \][/tex]

Thus, the values of [tex]\( A \)[/tex] and [tex]\( B \)[/tex] are:
[tex]\[ A = -2 \quad \text{and} \quad B = 3 \][/tex]

Therefore, the correct answer is:
[tex]\[ (-2, 3) \][/tex]