Question

a) (1/3)^x = 1/729

b) (1/3-1/2)^x-1 = 1/36

c) 25/5^x =1/125

d) (-7)^2n-1/49 = -343

Answer 1

a)\(\dfrac{1}{3}^x=\dfrac{1}{729}\)

\(\dfrac{1}{3}^x=\dfrac{1}{3}^6\)

Suy ra x=6

vậy x=6

b)\(\left(\dfrac{1}{3}-\dfrac{1}{2}\right)^x=\dfrac{1}{36}\)

\(\left(-\dfrac{1}{6}\right)^x\)=\(\dfrac{1}{6}^2\)

Do đó x=2

Vậy x=2

c)\(\dfrac{25}{5}^x=\dfrac{1}{125}\)

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

Suy ra x=-3

Vậy x=-3

d)\(7^{2n-\dfrac{1}{49}}=-343\)

\(-7^{2n-\dfrac{1}{49}}=-7^3\)

Do đó \(2n-\dfrac{1}{49}=3\)

2n=\(\dfrac{148}{49}\)

n=\(\dfrac{74}{49}\)

vậy n=\(\dfrac{74}{49}\)

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