Câu 1: 

\(\dfrac{2}{5}-\dfrac{1}{4}+\dfrac{3}{10}=\dfrac{8}{20}-\dfrac{5}{20}+\dfrac{6}{20}=\dfrac{8-5+6}{20}=\dfrac{9}{20}\) 

Câu 2:

\(\dfrac{-2}{5}:\left(1-\dfrac{1}{10}\right)=\dfrac{-2}{5}:\dfrac{9}{10}=\dfrac{-2}{5}.\dfrac{10}{9}=\dfrac{-2.10}{5.9}=\dfrac{-20}{45}=\dfrac{-4}{9}\) 

Câu 3:

\(\dfrac{7}{8}.\dfrac{4}{9}+\dfrac{1}{14}:\dfrac{5}{14}=\dfrac{7}{18}+\dfrac{1}{5}=\dfrac{53}{90}\) 

Câu 4:

\(\dfrac{2}{7}.\dfrac{3}{11}+\dfrac{2}{7}.\dfrac{8}{11}\) 

\(=\dfrac{2}{7}.\left(\dfrac{3}{11}+\dfrac{8}{11}\right)\) 

\(=\dfrac{2}{7}.1\) 

\(=\dfrac{2}{7}\)

Câu 1

\(\dfrac{2}{5}\)-\(\dfrac{1}{4}\)+\(\dfrac{3}{10}\)= \(\dfrac{8}{20}\)-\(\dfrac{5}{20}\)+\(\dfrac{6}{20}\)=\(\dfrac{3}{20}\)+\(\dfrac{6}{20}\)=\(\dfrac{9}{20}\)

Câu 2

-\(\dfrac{2}{5}\):(1-\(\dfrac{1}{10}\))= -\(\dfrac{2}{5}\):\(\dfrac{9}{10}\)=-\(\dfrac{2}{5}\).\(\dfrac{10}{9}\)=-\(\dfrac{4}{9}\)

Câu 3

\(\dfrac{7}{8}.\dfrac{4}{9}+\dfrac{1}{14}:\dfrac{5}{14}\)= \(\dfrac{7}{8}.\dfrac{4}{9}+\dfrac{1}{14}.\dfrac{14}{5}\)=\(\dfrac{7.4}{4.2.9}+\dfrac{1.14}{14.5}\)=\(\dfrac{7}{18}+\dfrac{1}{5}\)=\(\dfrac{35}{90}+\dfrac{18}{90}\)=\(\dfrac{53}{90}\)

Câu 4

\(\dfrac{2}{7}.\dfrac{3}{11}+\dfrac{2}{7}.\dfrac{8}{11}\)=\(\dfrac{2}{7}.\left(\dfrac{3}{11}+\dfrac{8}{11}\right)\)=\(\dfrac{2}{7}.1\)=\(\dfrac{2}{7}\)

a: =8/20-5/20+6/20=9/20

b: =-2/5:9/10=-2/5*10/9=-20/45=-4/9

c: =7/8*4/9+1/14*14/5

=28/72+1/5

=53/90

d: =2/7(3/11+8/11)

=2/7

\(a,\frac{-1}{9}.\frac{15}{22}.\frac{-9}{25}\)

\(=\frac{-1.15.\left(-9\right)}{9.22.25}\)

\(=\frac{3}{110}\)

\(b,\frac{-2}{7}.\left(\frac{5}{13}-\frac{9}{15}\right)-\frac{2}{7}.\frac{8}{13}\)

\(=\frac{-2}{7}.\left(\frac{5}{13}+\frac{8}{13}-\frac{3}{5}\right)\)

\(=\frac{-2}{7}.\left(1-\frac{3}{5}\right)\)

\(=\frac{-2}{7}.\frac{2}{5}\)

\(=\frac{-4}{35}\)

\(c,\frac{3}{10}.\left(\frac{-4}{9}+\frac{2}{5}\right)-\frac{3}{10}.\left(\frac{5}{9}-\frac{3}{5}\right)\)

\(=\frac{3}{10}.\left[\left(\frac{-4}{9}+\frac{2}{5}\right)-\left(\frac{5}{9}-\frac{3}{5}\right)\right]\)

\(=\frac{3}{10}.\left(\frac{-4}{9}+\frac{2}{5}-\frac{5}{9}+\frac{3}{5}\right)\)

\(=\frac{3}{10}.\left[\left(\frac{-4}{9}-\frac{5}{9}\right)+\left(\frac{2}{5}+\frac{3}{5}\right)\right]\)

\(=\frac{3}{10}.\left(-1+1\right)\)

\(=\frac{3}{10}.0\)

\(=0\)

\(d,\frac{4}{11}-\frac{5}{13}+\frac{7}{11}-\frac{8}{13}\)

\(=\left(\frac{4}{11}+\frac{7}{11}\right)+\left(\frac{-5}{13}-\frac{8}{13}\right)\)

\(=1-1\)

\(=0\)

Học tốt

\(\dfrac{81^6.9^5}{27^7.3^{11}}=\dfrac{\left(3^4\right)^6.\left(3^2\right)^5}{\left(3^3\right)^7.3^{11}}=\dfrac{3^{24}.3^{10}}{3^{21}.3^{11}}=\dfrac{3^3}{3}=3^2=9.\)

Cho đề rõ ràng nhé bạn!

Lời giải:

1.

$3^{x+2}+4.3^{x+1}=7.3^6$

$3^{x+1}.3+4.3^{x+1}=7.3^6$

$3^{x+1}(3+4)=7.3^6$

$3^{x+1}.7=7.3^6$

$\Rightarrow 3^{x+1}=3^6$

$\Rightarrow x+1=6$

$\Rightarrow x=5$

2.

$5^{x+4}-3.5^{x+3}=2.5^{11}$

$5^{x+3}.5-3.5^{x+3}=2.5^{11}$

$5^{x+3}(5-3)=2.5^{11}$

$2.5^{x+3}=2.5^{11}$

$\Rightarrow 5^{x+3}=5^{11}$

$\Rightarrow x+3=11$

$\Rightarrow x=8$

3.

$4^{x+3}-3.4^{x+1}=13.4^{11}$

$4^{x+1}.4^2-3.4^{x+1}=13.4^{11}$

$4^{x+1}.16-3.4^{x+1}=13.4^{11}$

$13.4^{x+1}=13.4^{11}$

$\Rightarrow 4^{x+1}=4^{11}$

$\Rightarrow x+1=11$
$\Rightarrow x=10$

a.\(\frac{3}{5}\)\(.\)\(\frac{1195}{1999}\)+ \(\frac{4}{1999}\)\(.\)\(\frac{3}{5}\)= \(\frac{3}{5}.\left(\frac{1195}{1999}+\frac{4}{1999}\right)\)= \(\frac{3}{5}.1\)= \(\frac{3}{5}\)

b. \(\frac{2}{3}\)\(:\)\(\frac{5}{7}\)\(.\)\(\frac{5}{7}\)\(:\)\(\frac{2}{3}\)\(+1934\)= \(\frac{2}{3}\).\(.\)\(\frac{7}{5}\)\(.\)\(\frac{5}{7}\)\(.\)\(\frac{3}{2}\)\(+\)\(1934\)= \(1\)\(+\)\(1934\)= \(1935\)

a] 3/5 . (1195/1999+4/1999)=tự tính

b] (2/3:2/3) . (5/7:5/7) + 1934=tự tính

Sr nha, mình bt làm hai câu đầu thôi.

16×2×3×7-5×7×16×2-7×8×4×8-4-6-7-8

=(16×2×7)×3-(16×2×7)×5-(7×8×4)×8-(4×7×8)×6

=224×3-224×5-224×8-224×6

=224×(3-5-8-6)

=224×(-16)

= -3584

mk ko biết là sai hay đúng đâu

\(A=\dfrac{5}{7}.\dfrac{5}{11}+\dfrac{5}{7}.\dfrac{8}{11}-\dfrac{5}{7}.\dfrac{2}{11}\)

\(A=\dfrac{5}{7}.\left(\dfrac{5}{11}+\dfrac{8}{11}-\dfrac{2}{11}\right)\)

\(A=\dfrac{5}{7}.\dfrac{5+8-2}{11}\)

\(A=\dfrac{5}{7}.\dfrac{11}{11}\)

\(A=\dfrac{5}{7}.1=\dfrac{5}{7}\)

\(B=\dfrac{1}{2}+\dfrac{1}{3}+\dfrac{1}{6}+\dfrac{1}{12}+\dfrac{1}{20}+\dfrac{1}{30}+\dfrac{1}{35}+\dfrac{1}{42}+\dfrac{1}{56}+\dfrac{1}{63}\)

\(B=\dfrac{95}{72}\)

\(C=\dfrac{4^6.9^5+6^9.120}{8^4-3^{12}-6^{11}}\)

\(C=\dfrac{\left(2^2\right)^3.\left(3^2\right)^5+\left(2.3\right)^9.2^3.3.5}{\left(2^3\right)^4.3^{12}-\left(2.3\right)^{11}}\)

\(C=\dfrac{2^{12}.3^{10}+2^9.3^9.2^3.3.5}{2^{12}.3^{12}-2^{11}.3^{11}}\)

\(C=\dfrac{2^{12}.3^{10}.\left(1+5\right)}{2^{11}.3^{11}.5}\)

\(C=\dfrac{2.6}{5.3}=\dfrac{12}{15}=\dfrac{4}{5}\)