Toán Lớp 6: Tìm x
a, (4x-5)^2 +34=70
b, (x-13)^28-9(x-13)^26=0
c, (x+17)^18=25.(x+7)
d, 5^x-3 + 5^x-4 = 150
25^x-4 = 125^6
Leave a reply
Register Now
Login
Lost Password
Lost your password? Please enter your email address. You will receive a link and will create a new password via email.
Toán Lớp 6: Tìm x
a, (4x-5)^2 +34=70
b, (x-13)^28-9(x-13)^26=0
c, (x+17)^18=25.(x+7)
d, 5^x-3 + 5^x-4 = 150
25^x-4 = 125^6
Comments ( 1 )
a){\left( {4x – 5} \right)^2} + 34 = 70\\
\Leftrightarrow {\left( {4x – 5} \right)^2} = 36\\
\Leftrightarrow \left[ \begin{array}{l}
4x – 5 = 6\\
4x – 5 = – 6
\end{array} \right.\\
\Leftrightarrow \left[ \begin{array}{l}
x = \dfrac{{11}}{4}\\
x = \dfrac{{ – 1}}{4}
\end{array} \right.\\
Vậy\,x = – \dfrac{1}{4};x = \dfrac{{11}}{4}\\
b){\left( {x – 13} \right)^{28}} – 9{\left( {x – 13} \right)^{26}} = 0\\
\Leftrightarrow {\left( {x – 13} \right)^{26}}.\left[ {{{\left( {x – 13} \right)}^2} – 9} \right] = 0\\
\Leftrightarrow \left[ \begin{array}{l}
x – 13 = 0\\
x – 13 = 3\\
x – 13 = – 3
\end{array} \right.\\
\Leftrightarrow \left[ \begin{array}{l}
x = 13\\
x = 16\\
x = 10
\end{array} \right.\\
Vậy\,x = 10;x = 13;x = 16\\
c){\left( {x + 17} \right)^{18}} = 25\left( {x + 7} \right)\\
\Leftrightarrow \left( {x + 7} \right).\left[ {{{\left( {x + 17} \right)}^{17}} – 25} \right] = 0\\
\Leftrightarrow \left[ \begin{array}{l}
x = – 7\\
{\left( {x + 17} \right)^{17}} = 25
\end{array} \right.\\
\Leftrightarrow \left[ \begin{array}{l}
x = – 7\\
x = – 17 + \sqrt[{17}]{{25}}
\end{array} \right.\\
d){5^{x – 3}} + {5^{x – 4}} = 150\\
\Leftrightarrow {5^{x – 4}}.\left( {5 + 1} \right) = 150\\
\Leftrightarrow {5^{x – 4}} = 25\\
\Leftrightarrow x – 4 = 2\\
\Leftrightarrow x = 6\\
Vậy\,x = 6\\
e){25^{x – 4}} = {125^6}\\
\Leftrightarrow {\left( {{5^2}} \right)^{x – 4}} = {\left( {{5^3}} \right)^6}\\
\Leftrightarrow 2\left( {x – 4} \right) = 3.6\\
\Leftrightarrow x – 4 = 9\\
\Leftrightarrow x = 13\\
Vậy\,x = 13
\end{array}$