Solving Exponential Equations

Using properties and logarithms to solve

Solving Exponential Equations

Strategy 1: Same Base

If you can write both sides with the same base, set exponents equal.

Example: 2x=82^x = 8 2x=232^x = 2^3 x=3x = 3

Strategy 2: Take Logarithms

When bases can't match, use logarithms:

Example: 3x=73^x = 7 ln(3x)=ln(7)\ln(3^x) = \ln(7) xln(3)=ln(7)x \ln(3) = \ln(7) x=ln(7)ln(3)x = \frac{\ln(7)}{\ln(3)}

Properties Used

Power Property: log(ab)=blog(a)\log(a^b) = b \log(a)

One-to-One Property: If bx=byb^x = b^y, then x=yx = y

Common Equations

Form: abcx=da \cdot b^{cx} = d

Steps:

  1. Isolate the exponential term
  2. Take log of both sides
  3. Use power property
  4. Solve for xx

Example: 523x=405 \cdot 2^{3x} = 40 23x=82^{3x} = 8 23x=232^{3x} = 2^3 3x=33x = 3 x=1x = 1

📚 Practice Problems

1Problem 1easy

Question:

Solve: 5x=1255^x = 125

💡 Show Solution

Write 125 as a power of 5: 5x=535^x = 5^3

Since the bases are equal: x=3x = 3

Answer: x=3x = 3

2Problem 2medium

Question:

Solve: 4x=204^x = 20

💡 Show Solution

The bases don't match easily, so use logarithms:

ln(4x)=ln(20)\ln(4^x) = \ln(20)

Use power property: xln(4)=ln(20)x \ln(4) = \ln(20)

Solve for xx: x=ln(20)ln(4)2.161x = \frac{\ln(20)}{\ln(4)} \approx 2.161

Answer: x=ln(20)ln(4)x = \frac{\ln(20)}{\ln(4)} or approximately 2.1612.161

3Problem 3hard

Question:

Solve: 32x+1=483 \cdot 2^{x+1} = 48

💡 Show Solution

Step 1: Isolate the exponential 2x+1=162^{x+1} = 16

Step 2: Write 16 as a power of 2 2x+1=242^{x+1} = 2^4

Step 3: Set exponents equal x+1=4x + 1 = 4

Step 4: Solve x=3x = 3

Check: 323+1=324=316=483 \cdot 2^{3+1} = 3 \cdot 2^4 = 3 \cdot 16 = 48

Answer: x=3x = 3