Question

[_ Pé Nguyên's _]

B = \(\frac{3}{4x7}+\frac{3}{7x10}+..................+\frac{3}{73x76}\)

Bài này tính bằng cách hợp lí nha m.n

[ 200 - 18 : (372 : 3 . x - 1) ] - 28 = 166

Còn bài này tìm x 

Giúp mk nha m.n ,ai nhanh 3 tick nek ^ - ^

Answer 1

[Nguyễn Vũ Minh Hiếu]

\(B=\frac{3}{4.7}+\frac{3}{7.10}+...+\frac{3}{73.76}\)

\(\Leftrightarrow B=\frac{1}{4}-\frac{1}{7}+\frac{1}{7}-\frac{1}{10}+...+\frac{1}{73}-\frac{1}{76}\)

\(\Leftrightarrow B=\frac{1}{4}+\left(\frac{1}{7}-\frac{1}{7}\right)+\left(\frac{1}{10}-\frac{1}{10}\right)+...+\left(\frac{1}{73}-\frac{1}{73}\right)-\frac{1}{76}\)

\(\Leftrightarrow B=\frac{1}{4}-\frac{1}{76}=\frac{9}{38}\)

~ Hok tốt ~

Answer 2

[Nguyễn Vũ Minh Hiếu]

\(\left[200-18:\left(372:3.x-1\right)\right]-28=166\)

\(\Leftrightarrow200-18:\left(124.x-1\right)=166+28\)

\(\Leftrightarrow200-18:\left(124.x-1\right)=194\)

\(\Leftrightarrow18:\left(372:3.x-1\right)=200-194\)

\(\Leftrightarrow18:\left(124.x-1\right)=6\)

\(\Leftrightarrow124.x-1=18:6\)

\(\Leftrightarrow124.x-1=3\)

\(\Leftrightarrow124.x=3+1\)

\(\Leftrightarrow124.x=4\)

\(\Leftrightarrow x=4:124\)

\(\Leftrightarrow x=\frac{1}{31}\)

~ Hok tốt ~