Answer:
6.3 inches
Step-by-step explanation:
The Pythagorean theorem tells you the relationship between the sides of a right triangle.
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The envelope can be modeled as a right triangle whose legs (a, b) are the width and length, and whose diagonal (c) is the hypotenuse. The Pythagorean theorem tells you ...
a² +b² = c²
a² +3² = 7²
a² = 49 -9 = 40 . . . . . subtract 3²
a = √40 = 2√10 ≈ 6.3
The length of the envelope is about 6.3 inches.
