Caprice adds equations A and B to solve this system of equations. What makes this approach a valid method in general for solving a system of equations?
The method will give the correct solution, x = 3 and y = 1.
8(3) + 3(1) = 27
4(3)–3(1) = 9
Because the y-terms cancel:
(8x + 3y) + (4x–3y) = 8x + 4x + 3y–3y = 12x
As long as addition is used on both sides or subtraction is used on both sides, a true equation will remain true.
Adding a quantity like 8x + 3y to one side of an equation and another quantity like 27 to the other side maintains the equality if the two quantities are equal.