What is the formula for the midpoint between two points?
a) (x₁ + x₂)/2, (y₁ + y₂)/2
b) (x₁ - x₂)/2, (y₁ - y₂)/2
c) (x₁ + x₂)/2, (y₁ - y₂)/2
d) (x₁ - x₂)/2, (y₁ + y₂)/2