Question

Найдите значение выражения №425-430, СРОЧНО!

Answer 1

$frac{2a+b}{ab}- frac{2}{b}= frac{2a+b-2a}{ab}= frac{b}{ab}= frac{1}{a}$
при а=2/3  1/(2/3)=3/2=1,5

$frac{a-3b}{ab}- frac{1}{b}= frac{a-3b-a}{ab}=- frac{3b}{ab}=- frac{3}{a}$
при а=3/17  -3/(3/17)=-17

$frac{5a-4b}{ab}- frac{5}{b}= frac{5a-4b-5a}{ab}=- frac{4b}{ab}=- frac{4}{a}$
при а=16/5    -4/(16/5)=-5/4=-1,25

$frac{6a}{a^2-b^2}- frac{6}{a+b}= frac{6a}{(a-b)(a+b)}- frac{6}{a+b}= frac{6a-6(a-b)}{(a-b)(a+b)}= frac{6a-6a+6b}{a^2-b^2} = frac{6b}{a^2-b^2}$
при а=8, b=2     
$frac{6*2}{8^2-2^2}= frac{12}{64-4}= frac{12}{60}= frac{1}{5}=0,2$

$frac{45a}{25a^-16b^2}- frac{9}{5a+4b}= frac{45a}{(5a-4b)(5a+4b)}- frac{9}{5a+4b}= frac{45a-9(5a-4b)}{(5a-4b)(5a+4b)}=$
$= frac{45a-45a+36b}{(5a-b)(5a+b)}= frac{36b}{(5a-4b)(5a+4b)}$
при а=5, b=5
$frac{36*5}{(5*5-4*5)(5*5+4*5)}= frac{36*5}{5*45}= frac{36}{45}= frac{4}{5}=0,8$

$frac{7a}{a^2-4b^2}- frac{7}{a+2b}= frac{7a}{(a-2b)(a+2b)}- frac{7}{a+2b}= frac{7a-7(a-2b)}{(a-2b)(a+2b)}= frac{14b}{(a-2b)(a+2b)}$
при а=8, b=3
$frac{14*3}{(8-2*3)(8+2*3)}= frac{14*3}{2*14}= frac{3}{2}=1,5$