a) \(\frac{120^3}{40^3}=\left(\frac{120}{40}\right)^3=3^3=27\)

b) \(\frac{3^2}{0,375^2}=\left(\frac{3}{0,375}\right)^2=8^2=64\)

HỌC TỐT

Toán lớp 7???

\(a.\)\(\frac{120^3}{40^3}=\left(\frac{120}{40}\right)^3=3^3=27\)

\(b.\)\(\frac{3^2}{\left(0,375\right)^2}=\left(\frac{3}{0,375}\right)^2=8^2=64\)

~ Rất vui vì giúp đc bn ~

3³ = 27

3⁴= 81

8²= 64

bạn làm đúng rồi đó

bạn làm rất tốt .

thiếu Vậy ....

1. sai dấu nhé 

2.a, \(\frac{45^{10}.5^{20}}{75^{15}}=\frac{\left(3^2.5\right)^{10}.5^{20}}{\left(5^2.3\right)^{15}}=\frac{3^{20}.5^{30}}{5^{30}.3^{15}}=3^5=243\)

b, \(\frac{\left(0,8\right)^5}{\left(0,4\right)^6}=\frac{\left(\frac{4}{5}\right)^5}{\left(\frac{2}{5}\right)^6}=\frac{\left(\frac{2}{5}\cdot2\right)^5}{\left(\frac{2}{5}\right)^6}=\frac{\left(\frac{2}{5}\right)^5\cdot2^5}{\left(\frac{2}{5}\right)^5\cdot\frac{2}{5}}=2^5\div\frac{2}{5}=32\cdot\frac{5}{2}=80\)

c, \(\frac{2^{15}.9^4}{6^6.8^3}=\frac{2^{15}.3^8}{2^6.3^6.2^9}=\frac{2^{15}.3^2}{2^{15}}=3^2=9\)

Với \(k\in N;k\ne0\) ta có :

\(\frac{1}{\left(k+1\right)\sqrt{k}+k\sqrt{\left(k+1\right)}}=\frac{1}{\sqrt{k\left(k+1\right)}\left(\sqrt{k}+\sqrt{k+1}\right)}\)

\(=\frac{\sqrt{k+1}+\sqrt{k}}{\sqrt{k\left(k+1\right)}\left(\sqrt{k+1}-\sqrt{k}\right)\left(\sqrt{k+1}+\sqrt{k}\right)}=\frac{\sqrt{k+1}-\sqrt{k}}{\sqrt{k\left(k+1\right)}}\)

\(=\frac{1}{\sqrt{k}}-\frac{1}{\sqrt{k+1}}\)

Áp dụng ta có :

\(M=\frac{1}{\sqrt{1}}-\frac{1}{\sqrt{2}}+\frac{1}{\sqrt{2}}-\frac{1}{\sqrt{3}}+....+\frac{1}{\sqrt{120}}-\frac{1}{\sqrt{121}}=1-\frac{1}{11}=\frac{10}{11}\)

\(\frac{120^3}{40^3}\)= (120:40)³ = 3³ = 27

\(\frac{390^4}{130^4}\)=(390 : 130)⁴=3⁴ = 81

\(\frac{3^2}{\left(0,375\right)^2}\)= (3:0,375)² = 8² =64

ai giúp mk với

mai phải nộp bài rùi

a,\(\frac{120^3}{40^3}=\frac{120}{40}=3\)

b,\(\frac{390^4}{130^4}=\frac{390}{130}=3\)

c,\(\frac{3^2}{\left(0,375\right)^2}=\frac{3}{0,375}=8\)

\(198-3\left(x+40\right)=120\\ \Rightarrow3\left(x+40\right)=78\\ \Rightarrow x+40=26\\ \Rightarrow x=-14\)

\(PT\Leftrightarrow3x+120=78\Leftrightarrow3x=-42\Leftrightarrow x=-14\)

Vậy: ...

a) x = 44.             

b) x = 40.            

c) x = 95.             

d) x = 10.

a) x - 120: 30 = 40

    x    -40        =40

              x        =40+40

              x        =80

b) (x + 120) : 20 = 8

    (x+ 120)         = 8x20

     x+120           =160

     x                   = 160-120

     x                  = 40

c) (x + 5). 3 = 300

     x+5=300:3

     x+5=100

     x=100-5

     x=95

d) x.2 + 21 : 3= 27

    x.2   +7=27

      x.2   = 27-7

    x.2= 20

      x=20:2

      x=10