Yes, that is the famous first Pythagorean triplet: 3²+4²=5²
or
For three lengths to be able to form a triangle, it suffices that every one of those lengths is shorter than the sum and longer than the difference of the other two.
It is enough to check just one side.
So,
3 + 4 > 5
4 - 3 < 5
Your triangle is constructible.
-1 cus its -1 becus u -1 so u get -1
You put the values of x into the equation to work out y, so the y column would be -5, -1, 3, 7 (for question 6)
For question 7, the y column would be 2,2,0,-2
Use these values to draw the graphs :)