Ta có: \(\frac{3}{4}+\frac{1}{4}.\left(2x-1\right)=\frac{2}{5}:\frac{-1}{2}\)

=> \(\frac{3}{4}+\frac{1}{4}.\left(2x-1\right)=\frac{-1}{10}\)

=> \(\frac{1}{4}.\left(2x-1\right)=\frac{-1}{10}-\frac{3}{4}\)

=> \(\frac{1}{4}.\left(2x-1\right)=\frac{1}{4}\)

=> \(\left(2x-1\right)=\frac{1}{4}:\frac{1}{4}\)

=> \(2x-1=1=>2x=2=>x=1\)

=> 3/4 + 1/4 . (2x - 1) = -4/5

=> 1/4 . (2x - 1) = -4/5 - 3/4 = -31/20

=> 2x -1 = -31/20 : 1/4 = -31/5

=> 2x = -31/5 + 1 = -26/5

=> x = -26/5 : 2 = ?

Đến đó bạn tự tính nhé

Học Tốt !

a, \(\left|2x+1\right|=3\)

=> 2x + 1 = 3 hoặc 2x + 1 = -3

=> 2x = 3 - 1 hoặc 2x = -3 - 1

=> 2x = 2 hoặc 2x = -4

=> x = 1 hoặc x = -2

b, \(2\frac{1}{2}x+1\frac{1}{2}=2\frac{2}{3}\)

=> \(\frac{5}{2}x+\frac{3}{2}=\frac{8}{3}\)

=> \(\frac{5}{2}x=\frac{8}{3}-\frac{3}{2}\)

=> \(\frac{5}{2}x=\frac{16-9}{6}\)

=> \(\frac{5}{2}x=\frac{7}{6}\)

=> \(x=\frac{7}{6}:\frac{5}{2}=\frac{7}{6}\cdot\frac{2}{5}=\frac{7}{3}\cdot\frac{1}{5}=\frac{7}{15}\)

c, \(3\cdot5^{x-3}+1=16\)

=> 3 . 5^x-3 = 16 - 1

=> 3 . 5^x-3 = 15

=> 5^x-3 = 15 : 3

=> 5^x-3 = 5

=> x - 3 = 5 : 5

=> x - 3 = 1

=> x = 1 + 3 = 4

d, \((x-1)^2=25\)

=> \((x-1)^2=5^2\)

=> x - 1 = 5 hoặc x - 1 = -5

=> x = 6 hoặc x = -4

e, \((-2)^2+\left|3x+1\right|=(-28)\cdot7\)

=> 4 + |3x + 1| = -196

=> |3x + 1| = -196 - 4 = -200

=> |3x + 1| = -200

Không thỏa mãn điều kiện

\(c=5+5^2+5^3+...+5^{20}\)

\(c=5.1+5.5+5.5^2+...+5.5^{19}\)

\(c=5.\left(1+5+5^2+...+5^{19}\right)\)chia hết cho 5

#Học tốt

6,5 - \(\frac{9}{4}\) :     x + 

sorry lỡ bấm gửi trả lời

\(A=\frac{3}{2}-\frac{5}{6}+\frac{13}{12}-\frac{19}{20}+\frac{31}{30}-\frac{41}{42}+\frac{57}{56}-\frac{71}{72}+\frac{91}{90}-\frac{109}{110}\)

\(\Rightarrow A=\left(1+\frac{1}{2}\right)-\left(1-\frac{1}{6}\right)+\cdot\cdot\cdot+\left(1+\frac{1}{90}\right)-\left(1-\frac{1}{110}\right)\)

\(\Rightarrow A=1+\frac{1}{2}-1+\frac{1}{6}+\cdot\cdot\cdot+1+\frac{1}{90}-1+\frac{1}{110}\)

\(\Rightarrow A=\left[\left(1-1\right)+\frac{1}{2}+\frac{1}{6}\right]+\cdot\cdot\cdot+\left[\left(1-1\right)+\frac{1}{90}+\frac{1}{110}\right]\)

\(\Rightarrow A=\frac{1}{2}+\frac{1}{6}+\cdot\cdot\cdot+\frac{1}{90}+\frac{1}{110}\)

\(\Rightarrow A=\frac{1}{1\cdot2}+\frac{1}{2\cdot3}+\cdot\cdot\cdot+\frac{1}{9\cdot10}+\frac{1}{10\cdot11}\)

\(\Rightarrow A=1-\frac{1}{2}+\frac{1}{2}-\frac{1}{3}+\cdot\cdot\cdot+\frac{1}{10}-\frac{1}{11}\)

\(\Rightarrow A=1-\frac{1}{11}\)

\(\Rightarrow A=\frac{10}{11}\)

2x : 12= 85

2x = 85 * 12 

2x = 1020

2 . x = 1020

    x  = 1020 : 2

    x  =  510

CHÚ Ý: dấu chấm là nhân nha

Đáp án 

x = 510

Học tốt

Bài 1: 1) (-x + y - z) - (x + y - z) = -x + y - z - x - y + z = (-x - x) + (y - y) - (z - z) = -2x

2) -(x - 2y + z) - (-x + 2y + z) = -x  + 2y - z + x - 2y - z = (-x + x) + (2y - 2y) - (z + z) = -2z

3) x(y + 1) - x(y - 1) = xy + x - xy + x = ( xy - xy) + (x + x) = 2x

4) 2(x + y) - 2(x - y) = 2(x + y - x + y) = 2.[(x - x) + (y + y) = 2. 2y = 4y

Bài 2. 1) xy - x + 5y - 5 = x(y - 1) + 5(y - 1) = (x + 5)(y - 1)

2) 2m - ma + an - 2n = m(2 - a) + n(a - 2) = m(2 - a) - n(2 - a) = (m - n)(2 - a)