4.4.6 Distance Between Two Parallel Lines

The Formula

For parallel lines $ax + by + c_1 = 0$ and $ax + by + c_2 = 0$:

$$\text{Distance} = \frac{|c_1 - c_2|}{\sqrt{a^2 + b^2}}$$

Tip: The line equation is usually a Pythagorean triple (3-4-5, 5-12-13) to simplify the calculation. You don’t need to move constants to exactly match the formula since you’re taking absolute values.

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Problem Set 4.4.6

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