1: =>0,5:(0,4-x)=2,5

=>0,4-x=0,5/2,5=0,5

=>x=0,4-0,5=-0,1

2: =>x*(3,6+6,4)=18,9

=>10x=18,9

=>x=1,89

3: =>(9,4+5,3):x=14

=>14,7:x=14

=>x=14,7/14=1,05

a) Ta có: \(6x\left(x-5\right)+3x\left(7-2x\right)=18\)

\(\Leftrightarrow6x^2-30x+21x-6x^2=18\)

\(\Leftrightarrow-9x=18\)

hay x=-2

Vậy: S={-2}

b) Ta có: \(2x\left(3x+1\right)+\left(4-2x\right)\cdot3x=7\)

\(\Leftrightarrow6x^2+2x+12x-6x^2=7\)

\(\Leftrightarrow14x=7\)

hay \(x=\dfrac{1}{2}\)

Vậy: \(S=\left\{\dfrac{1}{2}\right\}\)

c) Ta có: \(0.5x\left(0.4-4x\right)+\left(2x+5\right)\cdot x=-6.5\)

\(\Leftrightarrow0.2x-2x^2+2x^2+5x=-6.5\)

\(\Leftrightarrow5.2x=-6.5\)

hay \(x=-\dfrac{5}{4}\)

Vậy: \(S=\left\{-\dfrac{5}{4}\right\}\)

d) Ta có: \(\left(x+3\right)\left(x+2\right)-\left(x-2\right)\left(x+5\right)=6\)

\(\Leftrightarrow x^2+5x+6-\left(x^2+3x-10\right)=6\)

\(\Leftrightarrow x^2+5x+6-x^2-3x+10=6\)

\(\Leftrightarrow2x+16=6\)

\(\Leftrightarrow2x=-10\)

hay x=-5

Vậy: S={-5}

e) Ta có: \(3\left(2x-1\right)\left(3x-1\right)-\left(2x-3\right)\left(9x-1\right)=0\)

\(\Leftrightarrow3\left(6x^2-5x+1\right)-\left(18x^2-29x+3\right)=0\)

\(\Leftrightarrow18x^2-15x+3-18x^2+29x-3=0\)

\(\Leftrightarrow14x=0\)

hay x=0

Vậy: S={0}

73/63

22/15

105/88

\(9,4\times3,2+9,4-9,4\times2,2\)

\(=9,4\times\left(3,2+1-2,2\right)\)

\(=9,4\times2\)

\(=18,4\)

9,4 * 3,2 + 9,4 * 2,2

=  30,08 + 20,68

=  50,78

~ Học tốt ~

Mình viết nhầm đề bài ,kết quả là 18,4 nha 

~ Học tốt ~

<=>\(\dfrac{\left(3x-0,4\right)15}{30}+\dfrac{\left(1,5-2x\right)10}{30}=\dfrac{\left(x+0,5\right)6}{30}\)

=>\(\left(3x-0,4\right)15+\left(1,5-2x\right)10=\left(x+0,5\right)6\)

<=>\(45x-6+15-20x=6x+3\)

<=>\(45x-20x-6x=6+3-15\)

<=>\(19x=-6\)

<=>\(x=\dfrac{-6}{19}\)

A/ \(2x+5=20-3x\Leftrightarrow2x+3x=20-5\)\(\Leftrightarrow5x=15\Leftrightarrow x=\frac{15}{5}=3\)

KL: ...................................

B/ \(2x+12=8.27 \Leftrightarrow 2x=8.27-12=204 \\\ \Leftrightarrow x=102 \\\ KL:.................\)

C/ \(13-2y=y-2 \Leftrightarrow y+2y=13+2 \Leftrightarrow 3y=15 \\\ \Leftrightarrow y=5 \\\ KL: ......................\)

D/ \(3+2,5x+2,6=2x+5+0,5 \Leftrightarrow 2,5x-2x=5+0,4-3-2,6 \\\ \Leftrightarrow 0,5x=-0,2 \Leftrightarrow x=-0,4 \\\ KL:....................\)

Đây nhé!

= 9,4 x 90 + 9 x 9,4 + 9,4 x 1

= 9,4 x (90+9+1)

= 9,4 x 100

= 940

Bài làm  

   9,4 × 90 + 9 × 9,4 + 9,4

= 9,4 x ( 90 + 9 + 1 )

= 9,4 x 100

= 940

# Chúc bạn học tốt #

9,4 * 90 + 9 * 9,4 + 9,4

= 9,4 * 90 + 9 * 9,4 + 9,4 * 1

= 9,4 * ( 90 + 9 + 1 )

= 9,4 * 100

= 940