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Đặt x2 + 6x - 7 = 0
=> x2 - x + 7x - 7 = 0
=> x(x - 1 ) + 7 ( x-1) = 0
=> (x-1) . ( x+7) = 0
=> \(\left[{}\begin{matrix}x-1=0\\x+7=0\end{matrix}\right.=>\left[{}\begin{matrix}x=1\\x=-7\end{matrix}\right.\)
Vậy nghiệm của đa thức trên là 1 hoặc -7
a)\(\dfrac{0,4}{x}=\dfrac{x}{0,9}\Rightarrow x^2=0,4.0,9=0,36\Rightarrow x=0,6;-0,6\)
\(b)\dfrac{0,2}{1\dfrac{1}{5}}=\dfrac{\dfrac{2}{3}}{6x+7}\Rightarrow6x+7=\dfrac{1\dfrac{1}{5}.\dfrac{2}{3}}{0,2}=4\Rightarrow6x=-3\Rightarrow x=-\dfrac{3}{6}=-\dfrac{1}{2}\)
c)\(\dfrac{13\dfrac{1}{3}}{1\dfrac{1}{3}}=\dfrac{26}{2x+1}\Rightarrow2x+1=\dfrac{1\dfrac{1}{3}.26}{13\dfrac{1}{3}}=2,6\Rightarrow2x=1,6\Rightarrow x=0,8\)
d) mk ko hiểu
e)\(\dfrac{-2,6}{x}=\dfrac{-12}{42}\Rightarrow x=\dfrac{-2,6.42}{-12}=9,1\)
f)\(\dfrac{x^2}{6}=\dfrac{24}{25}\Rightarrow x^2=\dfrac{6.24}{25}=5,76\Rightarrow x=-2,4;2,4\)
n)mk chịu thua
xin lỗi bạn nha
1)(-1/2)^2:1/4-2.(-1/2)^3+căn 4
=1/4:1/4-2.-1/8+2
= 1-(-1/4)+2
=1+1/4+2=13/4
2) 3-(-6/7)^0+căn 9 :2
= 3-1+3:2
=3-1+3/2=7/2
3) (-2)^3+1/2:1/8-căn 25 + |-64|
= -8+4-5+64= 55
4) (-1/2)^4+|-2/3|-2007^0
= 1/16+2/3-1
= -13/48
5) = 178/495:623/495-17/60:119/120
= 2/7-2/7=0
6) [2^3.(-1/2)^3+1/2]+[25/22+6/25-3/22+19/25+1/2]
= [-1+1/2]+[(25/22-3/22)+(6/25+19/25)+1/2]
= -1/2+[1+1+1/2]
= -1/2+5/2=2
Mấy cái dấu chấm đó là nhân nha bn!
\(2\left(x+56\right)\left(x-6\right)=3^{25}:3^{22}\)
\(\Rightarrow2\left(x+56\right)\left(x-6\right)=3^{25-22}\)
\(\Rightarrow2\left(x+56\right)\left(x-6\right)=3^3\)
\(\Rightarrow\left(x+56\right)\left(x-6\right)=\dfrac{27}{2}\)
\(\Rightarrow x^2-6x+56x-336=\dfrac{27}{2}\)
\(\Rightarrow x^2+50x-336=\dfrac{27}{2}\)
\(\Rightarrow x^2+50x+625-961=\dfrac{27}{2}\)
\(\Rightarrow\left(x+25\right)^2=\dfrac{27}{2}+961\)
\(\Rightarrow\left(x+25\right)^2=\dfrac{1949}{2}\)
\(\Rightarrow\left[{}\begin{matrix}x+25=\sqrt{\dfrac{1949}{2}}\\x+25=-\sqrt{\dfrac{1949}{2}}\end{matrix}\right.\)
\(\Rightarrow\left[{}\begin{matrix}x=\sqrt{\dfrac{1949}{2}}-25\\x=-\sqrt{\dfrac{1949}{2}}-25\end{matrix}\right.\)
a, (\(\dfrac{9}{10}\) - \(\dfrac{15}{16}\)) \(\times\) ( \(\dfrac{5}{12}\) - \(\dfrac{11}{15}\) - \(\dfrac{7}{20}\))
= (\(\dfrac{72}{80}\) - \(\dfrac{75}{80}\)) \(\times\) (\(\)\(\dfrac{25}{60}\) - \(\dfrac{44}{60}\) - \(\dfrac{21}{60}\))
= - \(\dfrac{3}{80}\) \(\times\) (- \(\dfrac{2}{3}\))
= \(\dfrac{1}{40}\)
b, (-1)3 + (- \(\dfrac{2}{3}\))2 : 2\(\dfrac{2}{3}\) + \(\dfrac{5}{6}\)
= -13 + \(\dfrac{4}{9}\) : \(\dfrac{8}{3}\) + \(\dfrac{5}{6}\)
= -1 + \(\dfrac{4}{9}\) \(\times\) \(\dfrac{3}{8}\) + \(\dfrac{5}{6}\)
= -1 + \(\dfrac{1}{6}\) + \(\dfrac{5}{6}\)
= -1 + 1
= 0
\(a,\dfrac{x-1}{x+5}=\dfrac{6}{7}\\ \Leftrightarrow\left(x-1\right).7=6\left(x+5\right)\\ \Rightarrow7x-7=6x+30\\ \Rightarrow7x-6x=7+30\\ \Rightarrow x=37\)
Vậy \(x=37\)
\(b,\dfrac{x^2}{6}=\dfrac{24}{25}\\ \Leftrightarrow x^2.25=24.6\\ \Rightarrow x^2.5^2=144\\ \Rightarrow\left(5x\right)^2=144\\ \Rightarrow\left(5x\right)^2=\left(\pm12\right)^2\\ \Rightarrow\left\{{}\begin{matrix}5x=12\\5x=-12\end{matrix}\right.\Rightarrow\left\{{}\begin{matrix}x=\dfrac{12}{5}\\x=-\dfrac{12}{5}\end{matrix}\right.\)
Vậy \(x=\pm\dfrac{12}{5}\)
(7/3+7/2).x+25/6=22/7
x=-43/245
nha bạn chúc bạn học tốt nha
\(\left(\frac{7}{3}+\frac{7}{2}\right).x+\frac{25}{6}=\frac{22}{7}\)
\(\frac{35}{6}.x+\frac{25}{6}=\frac{22}{7}\)
\(\frac{35}{6}.x=\frac{22}{7}-\frac{25}{6}\)
\(\frac{35}{6}.x=-\frac{43}{42}\)
\(x=-\frac{43}{42}:\frac{35}{6}\)
\(x=-\frac{43}{245}\)