Hey guys, I solved this exercise but it just doesn't sound ok... Can anyone help me?
log2 (10x + 21) = 2 log2 (x+2)

log2 (10x + 21) = log2 (x+2)²
x² + 4x + 4 - 10x - 21 = 0
x² - 6x - 17 = 0

Bhaskara: 6 +- sqrt26 / 2
x' = 3 + 5,09 = x' = 8,09
x'' = 3 - 5,09 = x'' = -2,09

Conditions: x -2 and x -21/10 or x -2,1
So x' and x'' works.
Is that correct?
I have these options:

a) it has only one solution
b) it has more than 2 solutions
c) it has 2 solutions
d) it has infinite solutions

Question

Hey guys, I solved this exercise but it just doesn't sound ok... Can anyone help me?
log2 (10x + 21) = 2 log2 (x+2) 

log2 (10x + 21) = log2 (x+2)²
x² + 4x + 4 - 10x - 21 = 0
x² - 6x - 17 = 0

Bhaskara: 6 +- sqrt26 / 2
x' = 3 + 5,09 => x' = 8,09
x'' = 3 - 5,09 => x'' = -2,09

Conditions: x > -2 and x > -21/10 or x > -2,1
So x' and x'' works.
Is that correct?
I have these options:

a) it has only one solution
b) it has more than 2 solutions
c) it has 2 solutions
d) it has infinite solutions

anonymous · Answer

Problem is when I replace the values to confirm the answer, I get...
x' =>  101,9 = 101,8
x'' => -0,1 =0,0081

anonymous · Answer

Is that because of srqrt26? Or did I mess it up?

anonymous · Answer

Yeah, that's what I got... Thank you Rivera.