`@` `\text {Ans}`

`\downarrow`

`a.`

`3^n = 27` phải k c?

`3^n = 27`

`=> 3^n = 3^3`

`=> n=3`

Vậy, `n=3`

TH2 (đề):

`3n = 27`

`=> n = 27 \div 3`

`=> n=9`

Vậy, `n=9`

`b.`

TH1:

`5^n = 625`

`=> 5^n = 5^4`

`=> n = 4`

Vậy, `n=4`

TH2: 

`5n = 625`

`=> n = 625 \div 5`

`=> n = 125`

Vậy, `n=125`

`@` `\text {Ans}`

`\downarrow`

`1+2+3+4+5+6+7+8`

`= (1 +5) + (2+8) + (3+7) + (4+6)`

`= 6 + 10 + 10 + 10`

`= 36`

\(198+789+502+34\)

\(=\left(198+502\right)+\left(789+34\right)\)

\(=700+823\)

\(=1523\)

\(198+789+502+34\)

\(=\left(198+502\right)+\left(766+34\right)-23\)

\(=700+800-23\)

\(=1500-23\)

\(=1477\)

\(158+445+342+555\)

\(=\left(158+342\right)+\left(445+555\right)\)

\(=500+1000\)

\(=1500\)

\(158+445+342+555\)

\(=\left(158+342\right)+\left(445+555\right)\)

\(=500+1000\)

\(=1500\)

\(10+2x=45\div4^5\)

\(10+2x=45\div1024\)

\(10+2x=\dfrac{45}{1024}\)

\(2x=\dfrac{45}{1024}-10\)

\(2x=-\dfrac{10195}{1024}\)

\(x=-\dfrac{10195}{1024}:2=-\dfrac{10195}{2048}\)

\(714+382+286+318\)

\(=\left(714+286\right)+\left(382+318\right)\)

\(=1000+700\)

\(=1700\)

714+382+286+318

= (714+286)+(382+318)

= 1000+700

= 1700

\(15\cdot6\cdot4\cdot125\cdot8\)

\(=\left(15\cdot4\right)\cdot6\cdot\left(125\cdot8\right)\)

\(=60\cdot6\cdot1000\)

\(=60000\cdot6\)

\(=360000\)

15.6.4.125.8

= 3.5.2.3.4.(125.8)

= (5.2).3.3.4.1000

=10.36.1000

=360000

14.25.6.7

= 7.2.25.3.2.7

=(25.2.2).3.7.7

=100.3.7.7

=300.7.7

=2100.7

=14700

`@` `\text {Ans}`

`\downarrow`

`24*3*5*10`

`= 2^3*3*3*5*5*2`

`= 2^4*3^2*5^2`

`= 4^2*3^2*5^2`

`= (4*3*5)^2`

`= 60^2`

`= 3600`

\(24\cdot3\cdot5\cdot10\)

\(=3\cdot3\cdot2\cdot3\cdot5\cdot10\)

\(=\left(3\cdot3\cdot3\right)\cdot\left(2\cdot5\right)\cdot10\)

\(=27\cdot10\cdot10\)

\(=27\cdot100\)

\(=2700\)

2+4+6+8+...+(2x)=120

=> (1+2+3+4+...+x).2=120

=> 1+2+3+4+...+x = 120:2=60

=> (x+1).x : 2 = 60

=> (x+1).x=60.2 = 120

=> Không có x thỏa mãn

giúp tôi với tôi đang gấp , đi mà , năn nỉ đó . huhu