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Nguyễn Việt Lâm · Accepted Answer

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.$$\Rightarrow x+y+z=2+57+23=82$Câu trả lời: a.$2x^3-1=15$$\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$

Nguyễn Việt Lâm · Answer

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$$\Rightarrow\dfrac{a}{c}=\dfrac{a^2}{b^2}=\dfrac{b^2}{c^2}=\dfrac{a^2+b^2}{b^2+c^2}$ (đpcm)Câu trả lời: b.$\dfrac{\overline{ab}}{\overline{bc}}=\dfrac{b}{c}\Leftrightarrow\dfrac{10a+b}{10b+c}=\dfrac{b}{c}$$\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)

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