Question 607150
log x+log(x+21)=2
first determine domain
domain=x>0 and x>-21=x>0
log(x*(x+21))=2
log(x^2+21x)=2
x^2+21x=10^2
x^2+21x=100
x^2+21x-100=0
x^2-4x+25x-100=0
x(x-4)+25(x-4)=0
(x+25)+(x-4)=0
(x+25)=0 or(x-4)=0
x=-25 or x=4
or
use quadratic formula
x^2+21x-100=0
x=(-21+or-square root of (441+400))/2
x=(-21+or-square root of (841))/2
x=(-21+or- 29)/2
x=(-21+29)/2 or x=(-21-29)/2
x=8/4  or x=-50/2
x=4 or x=-25
but the solution is only x=4 since -25 is not in the domain
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