Question

Tìm x :

\(a,5^x=125\)

\(b,3^{2x}=81\)

\(c,5^{2x-3}-2.5^2=5^2.3\)

Answer 1

a,5^x=125

=>5^x=5^3

=>x=3

b,3^2x=81

=>3^2x=3^4

=>2x=4

=>x=4:2=2

c,5^2x-3-2*5^2=5^2+3

5^2x-3-50=75

5^2x-3=75+50=125

5^2x-3=5^3

=>2x-3=3

=>2x=3+3=6

=>6:2=3

k cho mk nhé

Answer 2

\(a,125=5\cdot5\cdot5=5^3\Leftrightarrow x=3\)

\(b,81=3\cdot3\cdot3\cdot3=3^4\Leftrightarrow2x=4\Leftrightarrow x=4:2\Leftrightarrow x=2\)

\(c,5^{2x-3}-2\cdot5^2=5^2\cdot3\)

\(\Leftrightarrow5^{2x-3}=2\cdot5^2+5^2\cdot3\)

\(\Leftrightarrow5^{2x-3}=5^2\cdot\left(2+3\right)\)

\(\Leftrightarrow5^{2x-3}=5^2\cdot5\Leftrightarrow5^{2x-3}=5^3\)

\(\Leftrightarrow2x-3=3\Leftrightarrow2x=3+3\Leftrightarrow2x=6\Leftrightarrow x=6:2\Leftrightarrow x=3\)

Answer 3

a.Ta thấy :\(125=5^3\)\(\Rightarrow x=3\)

b.Ta thấy : \(81=3^4\)\(\Rightarrow2x=4\Rightarrow x=2\)

c.Ta có:

\(5^{2x-3}-2.5^2=5^2.3\)

\(5^{2x-3}=5^2.3+5^2.2\)

\(5^{2x-3}=5^2.5\)

\(5^{2x-3}=5^3\)

\(\Rightarrow2x-3=3\)

     \(2x=3+3\)

     \(2x=6\)

     \(\Rightarrow x=3\)