You can start by doing this:
4 = 0.5x(5 - y)²
---> 8 = x(5 - y)² ---> 8/x = (5 - y)² ---> ± √(8)/√(x) = 5 - y
---> y = 5 ± √(8)/√(x) ---> y = 5 ± 2√(2)/√(x)
similarly:
1 = 0.5x(3 - y)²
---> 2 = x(3 - y)² ---> 2/x = (3 - y)² ---> ± √(2)/√(x) = 3 - y
---> y = 3 ± √(2)/√(x)
Choosing one from each group and setting them equal to each other:
5 - 2√(2)/√(x) = 3 - √(2)/√(x)
---> 2 = 2√(2)/√(x) - √(2)/√(x) ---> 2 = √(2)/√(x) ---> 2√(x) = √(2) ---> √(x) = √(2)/2
---> x = 2/4 ---> x = 1/2
When x = 1/2, y = 3 - √(2)/√(1/2) ---> y = 3 - √(4) ---> y = 3 - 2 = 1
So, one answer is (0.5, 1).
But, I choose only one possibility from each. Now, it's up to you to choose the other 3 possibilities (not all may work).
This is rather sketchy; if you want further help, please ask.
