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The sum of the lengths of any two sides of a triangle must be greater than the third side.
If a triangle has one side that is 17 cm and a second side that is 4 cm less than twice the third side,
what are the possible lengths for the second and third sides?
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Let x be the length o the third side.
Then the length of the second side is (2x-4).
According to the "triangle inequalities", these three inequalities should be in the place
17 + (2x-4) > x, (1)
(2x-4) + x > 17, (2)
17 + x > 2x-4. (3)
Inequality (1) is always valid and does not bring any restrictions.
Inequality (2) is x > = 7.
Inequality (3) is x < 21.
Answer. The third side length must be between 7 and 21 (excluding the ends).
The second side must be longer than 7. In addition, the second side must be "4 cm less than twice the third side".