[Toán lớp 6]Tìm x/ Tính hợp lý

H

harrypham

$ \dfrac{x-1}{9}= \dfrac{8+x}{3} \implies 9(8+x)=3(x-1) \implies 72+9x=3x-3 \implies 3x-9x=72+3 \implies -6x=75 \implies x= \dfrac{-25}{2}$.

$2B= \dfrac{2}{1.3}+ \dfrac{2}{3.5}+...+ \dfrac{2}{99.101}$
$\implies 2B= \dfrac{1}{1}- \dfrac{1}{3}+ \dfrac{1}{3}- \dfrac{1}{5}+...+ \dfrac{1}{99}- \dfrac{1}{101}= 1- \dfrac{1}{101}$
$\implies B= \dfrac{1}{2}- \dfrac{1}{202}$

$C=15. \dfrac{1}{2}. \dfrac{2}{3}. \dfrac{3}{4}... \dfrac{14}{15}= 15.\dfrac{1}{15}=1 $.
 
You must log in or register to reply here.
Top Bottom