\(\left(x-\dfrac{2}{7}\right)\left(x+\dfrac{3}{4}\right)=0\)

\(\Leftrightarrow\left[{}\begin{matrix}x=\dfrac{2}{7}\\x=-\dfrac{3}{4}\end{matrix}\right.\)

\(\Rightarrow\dfrac{x}{15}=\dfrac{y}{20}=\dfrac{z}{28}\)

\(\Rightarrow\dfrac{2x}{30}=\dfrac{3y}{60}=\dfrac{z}{28}\)

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

\(\dfrac{2x}{30}=\dfrac{3y}{60}=\dfrac{z}{28}=\dfrac{2x+3y-z}{30+60-28}=\dfrac{186}{62}=3\)

\(\Rightarrow\left\{{}\begin{matrix}x=45\\y=60\\z=84\end{matrix}\right.\)

Vậy ...

\(\sqrt{3-\sqrt{2}}.\sqrt{3+\sqrt{2}}=\sqrt{3^2-\sqrt{2}^2}=\sqrt{7}\)

bấm nhầm số á e

a) \(\left(\sqrt{3}+1\right)^2=\sqrt{3}^2+2\sqrt{3}+1=4+2\sqrt{3}\)

b) \(\left(\sqrt{3}+1\right)\left(\sqrt{3}-1\right)=\sqrt{3}^2-1=2\)

\(7^x.49=7^{90}\)

\(7^x.7^2=7^{90}\)

\(7^{x+2}=7^{90}\)

\(x+2=90\)

\(x=98\)

\(\left(\dfrac{1}{64}\right)^9.12^{27}=\dfrac{12^{27}}{64^9}=\dfrac{4^{27}.3^{27}}{64^9}=\dfrac{\left(4^3\right)^9.3^{27}}{64^9}=\dfrac{64^9.3^{27}}{64^9}=3^{27}\)

\(7^x.7^7=7^9\)

\(7^{x+7}=7^9\)

\(x+7=9\)

\(x=2\)