How do you solve log(5x+2)=log(2x-5)log(5x+2)=log(2x5)?

1 Answer
Dec 9, 2015

x= -7/3x=73

Explanation:

Given log(5x+2) = log(2x-5)log(5x+2)=log(2x5) common log- base 10

Step 1: Raised it to exponent using the base 10

10^(log5x+2) = 10^(log2x-5)10log5x+2=10log2x5

Step 2: Simplify, since 10^logA= A10logA=A
5x+2= 2x-55x+2=2x5

Step 3: Subtract color(red) 22 and color(blue)(2x)2x to both side of the equation to get
5x+2color(red)(-2)color(blue)(-2x)= 2x color(blue)(-2x)-5color(red)(-2)5x+222x=2x2x52
3x= -73x=7

Step 4: Dive both side by 3
(3x)/3 = -7/3 hArr x= -7/33x3=73x=73

Step 5: Check the solution

log[(5*-7/3)+2] = log[(2*-7/3) -5]log[(573)+2]=log[(273)5]
log(-35/3 + 6/3) = log(-14/3 -15/3)log(353+63)=log(143153)
log(-29/3) = log(-29/3)log(293)=log(293)

Both side are equal, despite we can't take a log of a negative number due to domain restriction log_b x = y, , x >0 , b>0logbx=y,,x>0,b>0
x= -7/3x=73 , assuming a complex valued logarithm