Question

BT3;Tìm x

a,2^x.4=128

b,2^x-26=6

c,27.3^x=3⁷

d,3^x=81

e,64.4^x=4⁵

g,49.7^x=2401

h,3⁴.3^x=3⁷

Answer 1

Bài 3:

a) Ta có: \(2^x\cdot4=128\)

\(\Leftrightarrow2^x=32\)

hay x=5

Vậy: x=5

b) Ta có: \(2^x-26=6\)

\(\Leftrightarrow2^x=32\)

hay x=5

Vậy: x=5

c) Ta có: \(27\cdot3^x=3^7\)

\(\Leftrightarrow3^x=\frac{3^7}{27}=\frac{3^7}{3^3}=3^4\)

hay x=4

Vậy: x=4

d) Ta có: \(3^x=81\)

\(\Leftrightarrow3^x=3^4\)

hay x=4

Vậy: x=4

e) Ta có: \(64\cdot4^x=4^5\)

\(\Leftrightarrow4^3\cdot4^x=4^5\)

\(\Leftrightarrow4^{x+3}=4^5\)

\(\Leftrightarrow x+3=5\)

hay x=2

Vậy: x=2

g) Ta có: \(49\cdot7^x=2401\)

\(\Leftrightarrow7^2\cdot7^x=7^4\)

\(\Leftrightarrow7^{x+2}=7^4\)

\(\Leftrightarrow x+2=4\)

hay x=2

Vậy: x=2

h) Ta có: \(3^4\cdot3^x=3^7\)

\(\Leftrightarrow3^{x+4}=3^7\)

\(\Leftrightarrow x+4=7\)

hay x=3

Vậy: x=3