\(a,\dfrac{4}{x}=\dfrac{8}{x+1}\left(x\ne0;x\ne-1\right)\Rightarrow4x+4=8x\\ \Rightarrow x=1\\ b,\dfrac{x}{7}=\dfrac{x+16}{35}\Rightarrow35x=7x+112\\ \Rightarrow28x=112\Rightarrow x=4\\ c,\dfrac{6}{x-3}=\dfrac{7}{x-5}\left(x\ne3;x\ne5\right)\Rightarrow6x-30=7x-21\\ \Rightarrow x=-9\\ d,\dfrac{44-x}{3}=\dfrac{x-12}{5}\Rightarrow220-5x=3x-36\\ \Rightarrow8x=256\Rightarrow x=32\)

D

D

Chọn D

A

A

A

a) Ta có: \(4\cdot\left(13-16\right)-\left(3-5\right)\cdot\left(-3\right)^2\)

\(=4\cdot13-4\cdot16+2\cdot9\)

\(=52-64+18\)

=6

b) Ta có: \(-\dfrac{2}{5}+\dfrac{7}{11}+\dfrac{-11}{10}+\dfrac{7}{-11}\)

\(=-\left(\dfrac{2}{5}+\dfrac{11}{10}\right)+\left(\dfrac{7}{11}-\dfrac{7}{11}\right)\)

\(=-\left(\dfrac{4}{10}+\dfrac{11}{10}\right)\)

\(=\dfrac{-15}{10}=\dfrac{-3}{2}\)

B

B

B

\(a,4^2=16>15=\left(\sqrt{15}\right)^2\Rightarrow4>\sqrt{15}\\ b,\left(\sqrt{27}\right)^2=27>25=5^2\Rightarrow\sqrt{27}>5\\ c,6^2=36>21=\left(\sqrt{21}\right)^2\Rightarrow6>\sqrt{21}\\ d,\left(\sqrt{79}\right)^2=79< 81=9^2\Rightarrow\sqrt{79}< 9\\ e,7^2=49>47=\left(\sqrt{47}\right)^2\Rightarrow7>\sqrt{47}\\ f,\left(\sqrt{123}\right)^2=123>100=10^2\Rightarrow\sqrt{123}>10\)

9/15+4/15= 13/15

2/1-7/12= 24/12-7/12= 17/12

10/21

5/6:5/1= 5/6x1/5= 5/30= 1/6

a: =3990-(463*72-39^2):15

=3990-2121=1869

b: =1995-963-172=860

c: =33/11-7/11=26/11

d: =3/2+5=13/2

`@` `\text {Answer}`

`\downarrow`

`a,`

`3990 - (463 \times 72 - 39 \times 39) \div 15`

`= 3990 - (33336 - 1521) \div 15`

`= 3990 - 31815 \div 15`

`= 3990 - 2121`

`= 1869`

`b,`

`1995 - 321 \times 3 - 6020 \div 35`

`= 1995 - 963 - 172`

`= 1032 - 172`

`= 860`

`c,`

`3 - 7/11`

`= 33/11 - 7/11`

`= 26/11`

`d,`

`1/4 \div 1/6 + 5`

`= 1/4 \times 6 + 5`

`= 3/2 + 5`

`= 13/2`