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Triangles are made in a row from matchsticks, as shown. Which rule gives the matchsticks for n triangles?

Class 7Formulas and Rules from PatternsAlgebra

A $2 n$
B $3 n$
C $3 n - 1$
D $2 n + 1$

Step-by-Step Solution

1 triangle: 3 sticks; 2 triangles: 5; 3 triangles: 7. Each new triangle adds 2 sticks, so

3 + 2 (n - 1) = 2 n + 1

.

Answer: D)

2 n + 1

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