How do we solve logsqrt(x - 8) + 1/2log(2x+ 1) = 1logx8+12log(2x+1)=1?

1 Answer
Sep 25, 2016

We have to start by simplifying using the rule alogn = logn^aalogn=logna.

logsqrt(x - 8) + logsqrt(2x + 1) = 1logx8+log2x+1=1

Now, use the rule logn + logm = log(n xx m)logn+logm=log(n×m)

log(sqrt(x - 8) xx sqrt(2x + 1)) = 1log(x8×2x+1)=1

log(sqrt(2x^2 - 15x - 8)) = 1log(2x215x8)=1

sqrt(2x^2 - 15x - 8) = 10^12x215x8=101

(sqrt(2x^2 - 15x - 8))^2 = (10^1)^2(2x215x8)2=(101)2

2x^2 - 15x - 8 = 1002x215x8=100

2x^2 - 15x - 108 = 02x215x108=0

2x^2 - 24x + 9x - 108 = 02x224x+9x108=0

2x(x - 12) + 9(x - 12) = 02x(x12)+9(x12)=0

(2x+ 9)(x - 12) = 0(2x+9)(x12)=0

x = -9/2 and 12x=92and12

However, x = -9/2x=92 is extraneous since it renders the square root negative, which is undefined in the real number system. Hence, the solution set is {12}{12}.

Hopefully this helps!