Question

Допоможіть будь ласка! Алгебра 8 клас. Треба знайти спільний чисельник

Answer 1

$\displaystyle\bf\\1)\\\\\dfrac{x+4}{2x-6} -\dfrac{x+1}{x-3} =\dfrac{x+4}{2(x-3)} -\dfrac{x+1}{x-3} =\dfrac{x+4-2\cdot(x+1)}{2(x-3)} =\\\\\\=\dfrac{x+4-2x-2}{2(x-3)} =\dfrac{2-x}{2x-6} \\\\\\2)\\\\\dfrac{3x}{4x-4} -\dfrac{5x}{7x-7} =\dfrac{3x}{4(x-1)} -\dfrac{5x}{7(x-1)} =\dfrac{3x\cdot 7-5x\cdot 4}{4\cdot 7\cdot (x-1)} =\\\\\\=\dfrac{21x-20x}{28(x-1)} =\dfrac{x}{28(x-1)}$

$\displaystyle\bf\\3)\\\\\dfrac{2}{a^{2} -9} -\dfrac{1}{a^{2}+3a } =\dfrac{2}{(a-3)(a+3)} -\dfrac{1}{a(a+3)}=\dfrac{2a-(a-3)}{a(a-3)(a+3)} =\\\\\\=\dfrac{2a-a+3}{a(a-3)(a+3)} =\dfrac{a+3}{a(a-3)(a+3)} =\dfrac{1}{a^{2}-3a }$