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Which set of three numbers could be the side lengths of a triangle?

A. 3, 5, 9
B. 3, 5, 7
C. 2, 4, 6
D. 2, 4, 8


Sagot :

To determine which set of three numbers can form the side lengths of a triangle, we need to use the triangle inequality theorem. This theorem states that for any three sides [tex]\(a\)[/tex], [tex]\(b\)[/tex], and [tex]\(c\)[/tex] of a triangle, the following conditions must all be true:

1. [tex]\(a + b > c\)[/tex]
2. [tex]\(b + c > a\)[/tex]
3. [tex]\(a + c > b\)[/tex]

We'll test each set of numbers against these conditions step-by-step:

### Option A: 3, 5, 9

1. [tex]\(3 + 5 > 9\)[/tex] ⟸ [tex]\(8 > 9\)[/tex] (False)
2. [tex]\(3 + 9 > 5\)[/tex] ⟸ [tex]\(12 > 5\)[/tex] (True)
3. [tex]\(5 + 9 > 3\)[/tex] ⟸ [tex]\(14 > 3\)[/tex] (True)

Since one of the conditions is false, the set {3, 5, 9} cannot form a triangle.

### Option B: 3, 5, 7

1. [tex]\(3 + 5 > 7\)[/tex] ⟸ [tex]\(8 > 7\)[/tex] (True)
2. [tex]\(3 + 7 > 5\)[/tex] ⟸ [tex]\(10 > 5\)[/tex] (True)
3. [tex]\(5 + 7 > 3\)[/tex] ⟸ [tex]\(12 > 3\)[/tex] (True)

All conditions are true, so the set {3, 5, 7} can form a triangle.

### Option C: 2, 4, 6

1. [tex]\(2 + 4 > 6\)[/tex] ⟸ [tex]\(6 > 6\)[/tex] (False)
2. [tex]\(2 + 6 > 4\)[/tex] ⟸ [tex]\(8 > 4\)[/tex] (True)
3. [tex]\(4 + 6 > 2\)[/tex] ⟸ [tex]\(10 > 2\)[/tex] (True)

Since one of the conditions is false, the set {2, 4, 6} cannot form a triangle.

### Option D: 2, 4, 8

1. [tex]\(2 + 4 > 8\)[/tex] ⟸ [tex]\(6 > 8\)[/tex] (False)
2. [tex]\(2 + 8 > 4\)[/tex] ⟸ [tex]\(10 > 4\)[/tex] (True)
3. [tex]\(4 + 8 > 2\)[/tex] ⟸ [tex]\(12 > 2\)[/tex] (True)

Since one of the conditions is false, the set {2, 4, 8} cannot form a triangle.

Since only option B satisfies the triangle inequality theorem, the set of numbers that could be the side lengths of a triangle is:

Option B: 3, 5, 7