Tính : x:5=X:6
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\(\Leftrightarrow7x\left(x+5\right)+\left(x-5\right)\left(x+5\right)=0\\ \Leftrightarrow\left(x-5\right)\left(7x+x+5\right)=0\\ \Leftrightarrow\left(x-5\right)\left(8x+5\right)=0\\ \Leftrightarrow\left[{}\begin{matrix}x=5\\x=-\dfrac{5}{8}\end{matrix}\right.\)
\(\Leftrightarrow x^2+x-5x-5-x^2-6x-9-6=0\\ \Leftrightarrow-10x-20=0\\ \Leftrightarrow x=-2\)

a: =152,3+7,7+2021,19-2021,19
=160
b: =7/15*3/14*20/13
\(=\dfrac{7}{14}\cdot\dfrac{3}{15}\cdot\dfrac{20}{13}=\dfrac{1}{2}\cdot\dfrac{1}{5}\cdot\dfrac{20}{13}=\dfrac{2}{13}\)
c: \(=\dfrac{7}{4}\left(\dfrac{13}{12}-\dfrac{10}{12}\right)+\dfrac{5}{6}=\dfrac{7}{16}+\dfrac{5}{6}=\dfrac{61}{48}\)

\(\left\{{}\begin{matrix}\dfrac{72}{x}+\dfrac{54}{y}=6\\x-y=6\end{matrix}\right.\left(x,y>0\right)< =>\left\{{}\begin{matrix}x=6+y\left(1\right)\\\dfrac{72}{\left(6+y\right)}+\dfrac{54}{y}=6\left(2\right)\end{matrix}\right.\)(x,y>0,y\(\ne-6\))
giải pt(2) \(\dfrac{72}{\left(6+y\right)}+\dfrac{54}{y}=6< =>\dfrac{72y+54\left(6+y\right)}{y\left(6+y\right)}=6\)
\(< =>\dfrac{126y+324}{y\left(6+y\right)}=6=>126y+324=6y\left(6+y\right)\)
\(< =>126y+324=36y+6y^2\)
\(< =>-6y^2+90y+324=0\)
\(\Delta=90^2-4\left(-6\right).324=15876>0\)
=>x1=\(\dfrac{-90+\sqrt{15876}}{2\left(-6\right)}=-3\left(loai\right)\)
x2=\(\dfrac{-90-\sqrt{15876}}{2\left(-6\right)}=18\left(TM\right)\)
=>x=x2=18 thay vào pt(1)=>x=6+18=24
vậy (x,y)=(24,18)

\(\dfrac{17}{22}+x=6\)
\(x=6-\dfrac{17}{22}\)
\(x=\dfrac{115}{22}\)

\(\dfrac{3}{4}\cdot\dfrac{2}{5}+\dfrac{3}{4}\cdot\dfrac{2}{5}\)
\(=\dfrac{3}{4}\cdot\dfrac{2}{5}\left(1+1\right)\)
\(=\dfrac{6}{20}\cdot2\)
\(=\dfrac{12}{20}=\dfrac{3}{5}\)

=> x=-11
y=11/5
x+xy-y\(=-11+\left(-\frac{11.11}{5}\right)-\frac{11}{5}=-\frac{187}{5}\)
Bạn tham khảo:
(x−5)(x−6) = 0
x : 5 = x : 6
= \(\frac{x}{5}\) = \(\frac{x}{6}\)
=> x = 0 vì 0 chia cho số nào cx = 0