The formula is called the “midpoint formula”. It looks like this
m=(x1+x2)/2 , (y1+y2)/2 where m means midpoint. In your case it looks like this.
Answer: 
Step-by-step explanation:
By the Pythagorean theorem, the unknown side has length

Therefore,

The range is 19-0=19 so therefore your answer is C.
The range is the largest number subtracted by the smallest number.
Answer:
A.
Step-by-step explanation:
you have to find the discriminant
b²-4ac for each equation
if discriminant < 0 no real solutions because will be negative under the squareroot whhan you try to find the roots
if discriminant = 0 there is only one solution
if discriminant > 0 two real solutions
for your given problems
A. discriminant =(-2)²-4*2*15 will be negative
X=31, the other post justifies, I just wanted to make it more accessible for if someone just needs the answer :)