Let call them x and y
x+y=7 and x*y=20
From the first you get x = 7 -y, put into the second get (7-y)*y=20
-y^2+7*y=20 or y^2-7+20=0
Delta = (-7)^2-4*1*20 = -31
y = (7-i*sqrt(31))/ 2 or y = (7+i*sqrt(31))/ 2
and
x = 7-y = (7+i*sqrt(31))/ 2 or x = (7-i*sqrt(31))/ 2
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