Toán Lớp 7: Bài 1: Tìm x
a. | x + 4 |= 2√2
b. 3.5 mủ 2x+1 -3.25 mủ x = 300
c. 5 mủ x+1 -2.5 mủ x = 375
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Toán Lớp 7: Bài 1: Tìm x
a. | x + 4 |= 2√2
b. 3.5 mủ 2x+1 -3.25 mủ x = 300
c. 5 mủ x+1 -2.5 mủ x = 375
Comments ( 1 )
a)\left| {x + 4} \right| = 2\sqrt 2 \\
\Leftrightarrow \left[ \begin{array}{l}
x + 4 = 2\sqrt 2 \\
x + 4 = – 2\sqrt 2
\end{array} \right.\\
\Leftrightarrow \left[ \begin{array}{l}
x = 2\sqrt 2 – 4\\
x = – 2\sqrt 2 – 4
\end{array} \right.\\
Vậy\,x = 2\sqrt 2 – 4;x = – 2\sqrt 2 – 4\\
b){3.5^{2x + 1}} – {3.25^x} = 300\\
\Leftrightarrow {3.5^{2x}}.5 – {3.5^{2x}} = 300\\
\Leftrightarrow {3.5^{2x}}.\left( {5 – 1} \right) = 300\\
\Leftrightarrow {3.5^{2x}}.4 = 300\\
\Leftrightarrow {5^{2x}} = 25\\
\Leftrightarrow {5^{2x}} = {5^2}\\
\Leftrightarrow 2x = 2\\
\Leftrightarrow x = 1\\
Vậy\,x = 1\\
c){5^{x + 1}} – {2.5^x} = 375\\
\Leftrightarrow {5^x}.5 – {2.5^x} = 375\\
\Leftrightarrow {5^x}.\left( {5 – 2} \right) = 375\\
\Leftrightarrow {5^x} = 375:3\\
\Leftrightarrow {5^x} = 125\\
\Leftrightarrow {5^x} = {5^3}\\
\Leftrightarrow x = 3\\
Vậy\,x = 3
\end{array}$