Question

1. Найдите значение выражения:

$ttcfrac{14b^2-c}{7b}-2b$ при $tt b=0,5; c=-14$


2. Упростите выражение:

$ttcfrac{5}{x-7}-cfrac{2}{x}-cfrac{3x}{x^2-49}+cfrac{21}{49-x^2}$

Answer 1

$displaystyle tt 1). frac{14b^{2}-c}{7b}-2b= frac{14b^{2}-c-14b^{2}}{7b}=- frac{c}{7b};\\\npu b=0,5 c=-14; -frac{c}{7b}= frac{14}{7cdot0,5}= frac{2}{0,5}=4;$

$displaystyle tt 2). frac{5}{x-7}- frac{2}{x}- frac{3x}{x^{2}-49}+ frac{21}{49-x^{2}}= frac{5x-2x+14}{x(x-7)}- frac{3x}{x^{2}-49}- frac{21}{x^{2}-49}=\\\{} = frac{3x+14}{x(x-7)}- frac{3x+21}{(x-7)(x+7)}= frac{(x+7)(3x+14)-x(3x+21)}{x(x-7)(x+7)}=\\\{} = frac{3x^{2}+21x+14x+98-3x^{2}-21x}{x(x-7)(x+7)}= frac{14x+98}{x(x-7)(x+7)}= frac{14(x+7)}{x(x-7)(x+7)}=\\\{} =frac{14}{x(x-7)};$