Find all pairs (x,y) of real numbers such that x + y = 10 and x^2 + y^2 = 56 + xy.
Step 1: Solve x + y = 10 for y: y = 10 - x
Step 2: Replace that value for y into the equation x2 + y2 = 56 + xy
---> x2 + (10 - x)2 = 56 + x(10 - x)
Step 3: Simplify that equation from step 2
Step 4: Use the quadratic formula to get the two solutions.
Step 5: Use those solution to get the two pairs that are the answer to the problem.