Question 1047960
Same as the DISTANCE FORMULA.


Your points A and B can form a diagonal of a rectangle on a cartesian system.  Your rectangle has a base of {{{1-(-3)=1+3=4}}} and a height of {{{2-0=2}}}.


One corner is the point  (-3,0) and the other corner is (1,2).


Can you plot the points, label them, and see the two congruent triangles?


I left out many steps and any graph.  You could work with this and find how the formula will fit.