Solve the Log Inequality: 2log₃x < log₃(x²+2x-12)

Question

Find the domain X where the inequality exists

2\log_3x<\log_3(x^2+2x-12)

Video Solution

Solution Steps

00:00 Solve
00:05 We'll use the power logarithm formula, raise the number to the coefficient
00:13 We'll equate the logarithms
00:23 We'll simplify what we can
00:28 We'll isolate X
00:43 And this is the solution to the question

Step-by-Step Solution

Let's solve the inequality 2log3x<log3(x2+2x12) 2\log_3x < \log_3(x^2+2x-12) .

  • Step 1: Apply the Power Property of Logarithms

The expression 2log3x 2\log_3x can be rewritten as log3(x2) \log_3(x^2) using the power property, which states alogb(x)=logb(xa) a\log_b(x) = \log_b(x^a) .

Thus, the inequality transforms to:

log3(x2)<log3(x2+2x12) \log_3(x^2) < \log_3(x^2 + 2x - 12)
  • Step 2: Remove the Logarithm by Ensuring Both Sides are Positive

Since log3(M)<log3(N)\log_3(M) < \log_3(N) implies M<NM < N when M>0M > 0 and N>0N > 0, the inequality becomes:

x2<x2+2x12 x^2 < x^2 + 2x - 12

Simplifying:

0<2x12 0 < 2x - 12

Add 12 to both sides:

12<2x 12 < 2x

Divide both sides by 2:

6<x 6 < x
  • Step 3: Consider the Domain Restrictions of the Logarithmic Terms

For both sides of the logarithmic inequality to be defined, we need to ensure:

  • x>0 x > 0
  • Expression inside the right logarithm is positive: x2+2x12>0 x^2 + 2x - 12 > 0

Solving x2+2x12>0 x^2 + 2x - 12 > 0 involves factorization:

(x+4)(x3)>0 (x + 4)(x - 3) > 0

This quadratic inequality gives critical points at x=4 x = -4 and x=3 x = 3 . Testing intervals around these points, the inequality holds when x<4 x < -4 or x>3 x > 3 . Considering the logarithmic condition x>0 x > 0 , we narrow it to x>3 x > 3 .

  • Step 4: Combine All Results

The combined condition from steps 2 and 3 yield:

6<x 6 < x

Therefore, the solution to the inequality is 6<x\boxed{6 < x}.

Answer

6 < x