Explanation:
a point on a coordinate grid always creates a right-angled triangle.
the straight distance from the origin (0, 0) is the Hypotenuse (the side opposite of the 90° angle).
the coordinate distances in x and y directions are the 2 legs.
Pythagoras :
c² = a² + b²
c being the Hypotenuse, a and b being the legs.
so,
(distance from origin)² = x² + y²
because the x, y coordinates are the coordinate distances from the origin in x and in y direction.
distance² = 8² + (-6)² = 64 + 36 = 100
distance = sqrt(100) = 10
the point is 10 units apart from the origin.