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Answer:
3.4 < x < 7.2
Step-by-step explanation:
The length of the third side of a triangle is always between the sum and difference of the lengths of the other two sides.
Here, the difference is 5.3 -1.9 = 3.4; the sum is 5.3 +1.9 = 7.2. So the length of the third side must satisfy ...
3.4 < x < 7.2
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Additional comment
The difference in side lengths is what you get when the shorter side is folded over the longer one. The excess of the longer over the shorter is the difference. If the triangle is to have non-zero area, the third side must be longer than that.
The sum of side lengths is what you bet when the two given sides are laid end-to-end. If the triangle is to have non-zero area, the third side must be shorter than that.
These statements are variations on the "triangle inequality", which states that the sum of any two sides must exceed the third. (That will always be the case if the sum of the shortest two sides exceeds the longest.)
