Please show me step by step how to solve this stupid thing. I've never seen one quite in this format so I'm at a complete loss as to how to solve it:
log X + log (X + 15) = 2
Thank you so much!
2007-03-23 03:23:15 · 3 answers · asked by Happy 3 in Science & Mathematics ➔ Mathematics
exponentiate both sides
x(x+15) = 100 [or e^2=100 if you mean natural logs]
x^2 + 15x - 100 = 0
( x-5)(x+20) = 0
so x = 5 or -20
2007-03-23 03:29:05 · answer #1 · answered by hustolemyname 6 · 1⤊ 0⤋
Depends on what the base is. Assuming that the base is 10
now we use log x + log (x+15) = log(x)(x+15) = 2
x(x+15) = 10^2 or x(x+15) = 100
or x^2 + 15x - 100 = 0
roots are 5,-20
Answer (5,-20)
2007-03-23 10:39:24 · answer #2 · answered by Nishit V 3 · 0⤊ 0⤋
express LHS as one log:
log[x(x+15)] = 2
10 to the power of both sides:
x(x+15) = 10² = 100
Solve the quadratic!
2007-03-23 10:29:15 · answer #3 · answered by Anonymous · 0⤊ 0⤋