22222222222222222

  Ta có :  

\(\frac{x^3}{8}\)= \(\frac{y^3}{64}\)= \(\frac{z^3}{216}\) \(\Rightarrow\)\(\frac{x^3}{2^3}\)= \(\frac{y^3}{4^3}\)= \(\frac{z^3}{6^3}\)\(\Rightarrow\)\(\frac{x^2}{2^2}\)=\(\frac{y^2}{4^2}\)=\(\frac{z^2}{6^2}\)

và có : \(^{x^2+y^2+z^2=224}\)

Áp dụng tính chất dãy tỉ số bằng nhau ta có:

\(\frac{x^2}{4}=\frac{y^2}{16}=\frac{z^2}{36}=\frac{x^2+y^2+z^2}{4+16+36}=\frac{224}{56}=4\)

=>    \(\frac{x^2}{4}=4\Rightarrow x^2=16\Rightarrow x\in4;-4\)​

\(\frac{y^2}{16}=4\Rightarrow y^2=64\Rightarrow y\in8:-8\)

\(\frac{z^2}{36}=4\Rightarrow z^2=144\Rightarrow z\in12:-12\)

Vì \(\frac{x^3}{8}=\frac{y^3}{64}=\frac{z^3}{216}\)nên x,y,z cùng dấu 

Vậy \(x,y,z\in\left(4;8;12\right);\left(-4;-8;-12\right)\)

trang web này để hỏi chứ ko để chơi đâu nha dương vật

8.2ⁿ +2ⁿ⁺¹ 

=2ⁿ .(8+2)

=2ⁿ.10 chia hết cho 10

=> 8.2ⁿ +2ⁿ⁺¹ chia hết cho 10

\(3^{n+3^{ }}-2.3^n+2^{n+5}-7.2^n\)

\(=3^n.\left(3^3-2\right)+2^n\left(2^5-7\right)\)

\(=3^n.25+2^n.25\)

=\(25.\left(3^n+2^n\right)\)chia hết cho 25

=>\(3^{n+3}-2.3^n+2^{n+5}-7.2^n\)

k cho mình nhé

\(\frac{15}{11.14}+\frac{15}{14.17}+\frac{15}{17.20}+.......+\frac{15}{74.77}\)

\(=5\left(\frac{3}{11.14}+\frac{3}{14.17}+\frac{3}{17.20}+.......+\frac{3}{74.77}\right)\)

\(=5\left(\frac{1}{11}-\frac{1}{14}+\frac{1}{14}-\frac{1}{17}+\frac{1}{17}-\frac{1}{20}+.....+\frac{1}{74}-\frac{1}{77}\right)\)

\(=5\left(\frac{1}{11}-\frac{1}{77}\right)\)

\(=5\left(\frac{7}{77}-\frac{1}{77}\right)\)

\(=5.\frac{6}{77}\)

\(=\frac{30}{77}\)