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Đáp án:
$15.$
$a)$
$\dfrac{4x + 1}{2} - \dfrac{3x + 2}{3}$
$= \dfrac{3(4x + 1) - 2(3x + 2)}{6}$
$= \dfrac{12x + 3 - 6x - 4}{6}$
$= \dfrac{6x - 1}{6}$
$b)$
ĐKXĐ: $x ≠ - 3; x ≠ 3$
$\dfrac{x + 3}{x} - \dfrac{x}{x - 3} + \dfrac{9}{x^2 - 3x}$
$= \dfrac{(x + 3)(x - 3) - x^2 + 9}{x(x - 3)}$
$= \dfrac{x^2 - 9 - x^2 + 9}{x(x- 3)}$
$= \dfrac{0}{x(x - 3)}$
$= 0$
$16.$
$a)$
ĐKXĐ: $x ≠ 0; y ≠ 0$
`1/x . \frac{6x}{y} = \frac{6x}{xy} = 6/y`
$b)$
ĐKXĐ: $y ≠ 0$
`\frac{2x^2}{y} . 3xy^2 = \frac{6x^3y^2}{y} = 6x^3y`
$c)$
ĐKXĐ: $x ≠ 0; y ≠ 0$
`\frac{15x}{7y^3} . \frac{2y^2}{x^2} = \frac{30xy^2}{7x^2y^2} = \frac{30}{7x}`
$d)$
ĐKXĐ: $x ≠ - 2; x ≠ 2$
`\frac{5x + 10}{4x - 8} . \frac{4 - 2x}{x + 2}`
`= \frac{5(x + 2)}{4(x - 2)} . \frac{- 2(x - 2)}{x + 2}`
`= - \frac{5}{2}`
