Question

How do you solve `logx+log(x+21)=2`?

Answer 1

`x=25`

Explanation:

`logx(x+21)=2`
`log(x^2+21x)=2`
`x^2+21x=10^2`
`x^2+21x-100=0`
`(x-4)(x+25)=0`
`x=4` and `x=-25`
`x=-25` is extraneous
`x=4`