The triangle inequality states that in a triangle, any two of the side lengths must add up to a length that is greater than the third. That is, if you have a triangle with sides a, b, and c, then a+b>c, a+c>b, and b+c>a.
In this case, we are given two lengths of a triangle. Let's call those two values a and b, where a>b.
Then we have that c
Now we can also use another inequality, a
Now we can apply these limits to all the individual questions.
1) 13 - 10 < c < 13 + 10. This simplifies down to 3 < c < 23
2) 12 - 5 < c < 12 + 5. This simplifies down to 7 < c < 17
3) 11 - 4 < c < 11 + 4. This simplifies down to 7 < c < 15
Hope it help!