`@` `\text {Ans}`
`\downarrow`
`a)`
`64^x \div 16^x = 256`
`=> (4^3)^x \div (4^2)^x = 256`
`=>`\(4^{3x}\div4^{2x}=4^4\)
`=>`\(4^{3x-2x}=4^4\)
`=>`\(4^x=4^4\)
`=> x = 4`
Vậy, `x = 4`
`b)`
\(\dfrac{-2401}{7^x}=-7\)
`=>`\(\dfrac{-7^4}{7^x}=-7\)
`=>`\(7^x=-7^4\div\left(-7\right)\)
`=> 7^x = 7^3`
`=> x = 3`
Vậy, `x = 3`
`c)`
\(\dfrac{625}{\left(-5\right)^x}=25\)
`=>`\(\dfrac{5^4}{\left(-5\right)^x}=5^2\)
`=>`\(\left(-5\right)^x=5^4\div5^2\)
`=> (-5)^x = 5^2`
`=> x =2`
Vậy, `x = 2`
a: =>4^x=256
=>x=4
b: =>7^x=343
=>x=3
c: =>(-5)^x=25
=>x=2