Question

bài 4 tìm x:

\(a,\left\{2.x+1\right\}^3=125\)

\(b,\left\{4.x-1\right\}^2=25.9\)

Answer 1

a) \(\left(2.x+1\right)^3=125\)

\(\Leftrightarrow\left(2.x+1\right)^3=5^3\)

\(\Leftrightarrow2.x+1=5\)

               \(2.x=5-1\)

               \(2.x=4\)

                    \(x=4:2\)

                     \(x=2\)

b) \(\left(4.x-1\right)^2=25.9\)

     \(\left(4.x-1\right)^2=225\)

\(\Leftrightarrow\left(2.x-1\right)^2=15^2\)

\(\Leftrightarrow2.x-1=15\)

\(\Rightarrow2.x=15+1\)

\(\Rightarrow2.x=16\)

\(\Rightarrow x=16:2\)

\(\Rightarrow x=8\)

Answer 2

a,(2x+1)³=5³

2x+1=5

2x=4

x=2

b,(4x-1)²=225

(4x-1)²=15²

4x-1=15

4x=16

x=4

Answer 3

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