Question

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

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

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

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

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

~ Hok tốt ~

Answer 2

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

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

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

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

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

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

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

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

\(\Leftrightarrow124.x=4\)

\(\Leftrightarrow x=4:124\)

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

~ Hok tốt ~

Answer 3

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

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

\(=1.\left(\frac{1}{4}-\frac{1}{76}\right)\)

\(=1.\frac{9}{38}=\frac{9}{38}\)

Answer 4

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

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

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

\(B=\frac{9}{38}\)

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

\(\Leftrightarrow200-18:\left(372:3x-1\right)=194\)

\(\Leftrightarrow18:\left(372:3x-1\right)=6\)

\(\Leftrightarrow372:3x-1=3\)

\(\Leftrightarrow372:3x=4\)

\(\Leftrightarrow3x=93\)

\(\Leftrightarrow x=31\)

Answer 5

#)Giải :

\(B=\frac{3}{4.7}+\frac{3}{7.10}+\frac{3}{10.13}+...+\frac{3}{73.76}\)

\(B=\frac{1}{4}-\frac{1}{7}+\frac{1}{7}-\frac{1}{10}+\frac{1}{10}-\frac{1}{13}+...+\frac{1}{73}-\frac{1}{76}\)

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

\(B=\frac{9}{38}\)

\(\left[200-18:\left(372\div3.x-1\right)\right]-28=166\)

\(\Leftrightarrow200-18\div\left(124x-1\right)=104\)

\(\Leftrightarrow18\div\left(124x-1\right)=96\)

\(\Leftrightarrow124x-1=0,1875\)

\(\Leftrightarrow124x=1,1875\)

\(\Leftrightarrow x=???\)

P/s : câu thứ hai cứ sao sao ý ???

Answer 6

Bài 2:.

Ko chép lại đề

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

[ 200-18:( 372:3. X-1)]= 166+28= 194

18;(124. X-1)] = 200-194 = 6

(124.x-1) = 18:6= 3

124.x= 3+1

124.x= 4

X= 4:124

X=...

Mk nghĩ đề sai r

Answer 7

#)Chết nhầm @@ cho mk sửa câu thứ hai nhé :v ( tưởng đề lỗi )

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

\(\Leftrightarrow200-18:\left(372:3.x-1\right)=194\)

\(\Leftrightarrow18:\left(372:3x-1\right)=6\)

\(\Leftrightarrow372:3x-1=3\)

\(\Leftrightarrow372:3x=4\)

\(\Leftrightarrow3x=93\)

\(\Leftrightarrow x=31\)