Answer: 20
Explanation:
x+y=5
x-y=4
---------
x=4+y
--------
(4+y)+y=5
4+y+y=5
4+2y=5
2y=1
y=0.5
x=4.5
x²-y²=(4.5)²-(0.5)²=20.25-0.25=20
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