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Chapter 1: Basics
Reciprocals
Two numbers that multiply to equal one
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Reciprocals

Two numbers are reciprocals when you multiply them together and get exactly 1.

Reciprocals are always inversely related. When one gets bigger, the other gets smaller.

4 slices × ¼ = 1 whole pizza
Change the number of slices
Number of slices

No matter how you slice it, the number of slices and the size of each slice are reciprocals. More slices means each piece is smaller. Multiply them and you always get 1 whole pizza.

This is the shape of a reciprocal relationship. As one value increases, the other drops toward zero but never reaches it.

Move along the curve

This curve is called 1/x. It never touches either axis. That is the signature shape of reciprocals.

Period and Frequency are the most important reciprocal pair in ultrasound. They will come up constantly. Click below for a preview.

Frequency ▸
Definition: How many wave cycles happen per second.

Example: Higher frequency means more cycles packed into the same amount of time.
Period ▸
Definition: How long one cycle takes to complete.

Example: When frequency goes up, each cycle has less time, so period goes down. They are reciprocals: Frequency x Period = 1.

Quick Check

Two numbers are reciprocals when they multiply to equal:
Frequency and Period are reciprocals. If frequency doubles, period:

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