a) 12/17 và 7/15

=>180/255 và 119/225

=>12/17<7/15

b)1999/2001 và 12/11

\(a,x-36:18=12-15\\ \Rightarrow x-2=-3\\ \Rightarrow x=-1\\ b,92-\left(17+x\right)=72\\ \Rightarrow17+x=20\\ \Rightarrow x=3\\ c,720:\left[41-\left(2x+5\right)\right]=40\\ \Rightarrow41-\left(2x+5\right)=18\\ \Rightarrow2x+5=23\\ \Rightarrow2x=18\\ \Rightarrow x=9\\ d,\left(x+2\right)^3-23=41\\ \Rightarrow\left(x+2\right)^3=64\\ \Rightarrow\left(x+2\right)^3=4^3\\ \Rightarrow x+2=4\\ \Rightarrow x=2\)

b: =>x+17=20

hay x=3

d: =>x+2=4

hay x=2

A = 1
B = 3
C = 9
D = 2

\(-15a+12\ge-15b+12\)

\(\Leftrightarrow-15a+12-12\ge-15b\)

\(\Leftrightarrow-15a\ge-15b\)

\(\Leftrightarrow\left(-1\right)\cdot\left(-15a\right)\le\left(-1\right)\cdot\left(-15b\right)\)

\(\Leftrightarrow15a\le15b\)

\(\Leftrightarrow a\le b\)

Vậy : \(a\le b\)

Ta có :

\(-15a+12\ge-15b+12\)\(2\)

\(\Rightarrow-15a+12+\left(-12\right)\ge-15b+12+\left(-12\right)\)

\(\Rightarrow-15a\ge-15b\)

\(\Rightarrow-15a.\frac{1}{-15}\le-15b.\frac{1}{-15}\)

\(\Rightarrow a\le b\)

\(-15a+12\ge-15b+12\)

\(\Rightarrow-15a\ge-15b\)\(\Rightarrow\left(-15a\right)-\left(-15b\right)\ge0\)

\(\Rightarrow-15a+15b\ge0\)\(\Leftrightarrow15\left(-a+b\right)\ge0\)

\(\Leftrightarrow-a+b\ge0\)\(\Leftrightarrow b-a\ge0\)\(\Leftrightarrow b\ge a\)

hay \(a\le b\)

A

A

A

Chọn A,D

b: Ta có: \(\dfrac{12}{5}:x+\dfrac{4}{3}=3+\dfrac{2}{3}\)

\(\Leftrightarrow\dfrac{12}{5}:x=3-\dfrac{2}{3}=\dfrac{7}{3}\)

hay \(x=\dfrac{12}{5}:\dfrac{7}{3}=\dfrac{36}{35}\)

a. \(=\left(\dfrac{12}{15}+\dfrac{3}{15}\right)+\left(\dfrac{4}{3}+\dfrac{5}{3}\right)+\left(\dfrac{1}{4}+\dfrac{3}{4}\right)\\ =1+2+1=4\)

b. \(x\times\dfrac{3}{4}=\dfrac{1\times3\times6\times5}{6\times5\times5\times3}\\ x\times\dfrac{3}{4}=\dfrac{1}{5}\\ x=\dfrac{1}{5}:\dfrac{3}{4}\\ x=\dfrac{4}{15}\)

a.

(12/15+3/15)+(4/3+5/3)+(1/4+3/4)

=1+3+1=5

b.X x 3/4=1/5

           X=1/5:3/4

           X=4/15

a. 36 + (-15) + 27 + (-36) + 15

= 36 - 15 + 27 - 36 + 15

= 36 - 36 - 15 + 15 + 27

= 0 - 0 + 27

= 27

b. -12 + 34 + (-28) + 12 + (-34)

= 34 - 12 - 28 + 12 - 34

= 34 - 34 - 12 + 12 - 28

= 0 - 0 - 28

= -28

c. -15 + 16 + (-25) + 34 + (-23)

= 16 - 15 - 25 + 34 - 23

= 16 + 34 - 15 - 15 - 23

= 50 - 30 - 23

= -3

d. -12 + 8 + 18 + (-17) + 81 + (-71) + 1

= 8 - 12 + 18 - 17 + 81 - 71 + 1

= -4 + 1 + 10 + 1

= -3 + 11

= 8

e. -284 + 184 + 35 + (-25)

= 184 - 284 + 35 - 25

= -100 + 10

= -90

Quá khen, quá khen

Bn chỉ cần bỏ phần mik bỏ ngoặc là làm tiếp thôi

Bài 2: 

a: \(\Leftrightarrow x-7=36\)

hay x=43