Question

[HSH :}}}}}]

 Các bạn giúp mik 1 câu cux đc ạ 

Answer 1

[Nguyễn Việt Lâm]

a.

\(2x^3-1=15\)

\(\Rightarrow2x^3=16\)

\(\Rightarrow x^3=8\)

\(\Rightarrow x=2\)

\(\Rightarrow\dfrac{x+16}{9}=\dfrac{2+16}{9}=2\)

\(\Rightarrow\left\{{}\begin{matrix}\dfrac{y-25}{16}=2\\\dfrac{z+9}{16}=2\end{matrix}\right.\) \(\Rightarrow\left\{{}\begin{matrix}y-25=32\\z+9=32\end{matrix}\right.\)

\(\Rightarrow\left\{{}\begin{matrix}y=57\\z=23\\\end{matrix}\right.\)

\(\Rightarrow x+y+z=2+57+23=82\)

Answer 2

[Nguyễn Việt Lâm]

b.

\(\dfrac{\overline{ab}}{\overline{bc}}=\dfrac{b}{c}\Leftrightarrow\dfrac{10a+b}{10b+c}=\dfrac{b}{c}\)

\(\Leftrightarrow\dfrac{10a+b}{10b+c}=\dfrac{b}{c}=\dfrac{10a+b-b}{10b+c-c}=\dfrac{10a}{10b}=\dfrac{a}{b}\)

\(\Rightarrow\dfrac{a}{b}=\dfrac{b}{c}\Rightarrow\dfrac{a}{b}.\dfrac{b}{c}=\left(\dfrac{a}{b}\right)^2=\left(\dfrac{b}{c}\right)^2\)

\(\Rightarrow\dfrac{a}{c}=\dfrac{a^2}{b^2}=\dfrac{b^2}{c^2}=\dfrac{a^2+b^2}{b^2+c^2}\) (đpcm)