Explanation:
so, if the text is correct, the 2 points are
(2, 3) and (-3, 15).
the length of the line segment is the distance between both points.
did this we use Pythagoras for right-angled triangles.
c² = a² + b²
c is the Hypotenuse and the distance between both points. a and b are the legs (enclosing the 90 degree angle), which are simply the differences of the x and the y coordinates.
so,
distance² = (2 - -3)² + (3 - 15)² = 5² + (-12)² = 25 + 144 = 169
distance = sqrt(169) = 13 = length of line segment