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# Logarithms watch

1. Solve the equation, 5^2x - (16 x 5^x) +63 = 0

Is this correct:

let 5^x = u

u^2 - 16 u +63 = 0

(u-7)(u-9)

5^x = 7 or 9

x log 5 = log63
x= log 63 /log 5
2. (Original post by Custardcream000)
Solve the equation, 5^2x - (16 x 5^x) +63 = 0

Is this correct:

let 5^x = u

u^2 - 16 u +63 = 0

(u-7)(u-9)

5^x = 7 or 9

x log 5 = log63
x= log 63 /log 5
The bold line above means that 5^x can be 7 or can be 9.

So you have two equations:

5^x = 7

5^x = 9

Solve both to get two solutions.
3. (Original post by notnek)
The bold line above means that 5^x can be 7 or can be 9.

So you have two equations:

5^x = 7

5^x = 9

Solve both to get two solutions.
thanks

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Updated: February 11, 2016
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