Could not do the 2nd one, but will update if I figure it out
The answer is the hypotenuse has a length of 5.
7) 2-9= -7 because, if you have two cookies and promised nine friends cookies, you would still owe 7 friends cookies or -7
8) -3 - (-4)= 1 because you owe 3 friends cookies, then you get 4 cookies and have one left over
9) 11 - (-12)= 23 because a negative plus a negative is a positive
Let

, so that

,

, and

. Then

Now let

, so that

. Then

Transform back to

to get

and again to get back a result in terms of

.