1,  17.( 85+15) -120 = 17. 100 -120 =1700 - 120 =1580

2, 

2³ . 17 - 2³ . 14

= 2³(17-14)

=2³. 3= 24

Cau 1)

21+(x+23)=50

X+23=50-21

X=29-23

X=6

Cau 2)

125+(x-100)=150

X-100=150-125

X=25+100

X=125

d) 135(-12 + 247) - 147(135 - 12)= -12.135 + 135.147 - 147.135 + 12.147 = (-12.135 + 12.147) + (135.147 - 147.135) = 12(-135 + 147) + 0 = -12.12 = -144

Bài 1:

a) [3.(-2) - (-8)].(-7) - (-2).(-5) = -7(-6 + 8) - 2.5= -7.2 - 2.5 = -2(7 + 5) = -2.12 = -24

1:

a: \(=\dfrac{-4}{7}+\dfrac{4}{7}+\dfrac{3}{7}-\dfrac{23}{34}-\dfrac{4}{5}=\dfrac{3}{7}-\dfrac{23}{34}-\dfrac{4}{5}=-\dfrac{1247}{1190}\)

b:

Sửa đề: \(\dfrac{-5}{13}+\dfrac{4}{19}+\dfrac{-8}{13}+\dfrac{15}{19}+\dfrac{45}{6}\) 

\(=\dfrac{-5}{13}-\dfrac{8}{13}+\dfrac{4}{19}+\dfrac{15}{19}+\dfrac{45}{6}=\dfrac{9}{2}\)

2:

a: x=2,4-0,4=2

b: =>2x=-1,5+0,8=-0,7

=>x=-0,35

c: =>x-16=-15

=>x=1

Ta có : 3(2x - 4) + 11 = -11

=> 3(2x - 4) = 0

Mà 3 khác 0 

Nên : 2x - 4 = 0

=> 2x = 4

=> x = 2

(102 + 112 + 122) : (132 + 142)

= (100 + 121 + 144) :( 169 + 196)

= 365: 365

= 1 

a) Ta có: \(2x=3y\Rightarrow\frac{x}{3}=\frac{y}{2}\)

               \(3y=5z\Rightarrow\frac{y}{5}=\frac{z}{3}\)

\(\Rightarrow\frac{x}{15}=\frac{y}{10}=\frac{z}{6}=\frac{x-2y+3z}{15-2.10+3.6}=\frac{65}{13}=5\)

\(\Rightarrow x=5.15=75\)

      \(y=5.10=50\)

      \(z=5.6=30\)

b) Ta có: \(\frac{x}{5}=\frac{y}{3};\frac{y}{7}=\frac{z}{4}\Rightarrow\frac{x}{35}=\frac{y}{21}=\frac{z}{12}=\frac{x+y-z}{35+21-12}=\frac{132}{44}=3\)

\(\Rightarrow x=3.35=105\)

      \(y=3.21=63\)

      \(z=3.12=36\)

c) Gọi \(\frac{x}{4}=\frac{y}{7}=k\)

\(\Rightarrow x=4k;y=7k\)

\(\Rightarrow x.y=4k.7k=28k^2=112\)

\(\Rightarrow k^2=112:28=4\)

\(\Rightarrow k=\pm2\)

\(\Rightarrow x=\pm2.4=\pm8\)

     \(y=\pm2.7=\pm14\)