x-y=10,xy=10 jadi x^4+y^4=?

x = y + 10, substitusikan pd xy = 10
(y + 10)y = 10
y^2 + 10y = 10
y^2 + 10y + 5^2 = 10 + 5^2
(y + 5)^2 = 35
y + 5 = +-√35
y = -5 +- √35
y = -5 + √35 atau y = -5 - √35
substitusikan pd salahsatu, didapat
x = 5 + √35 atau x = 5 - √35
misal diambil sepasang
x^4 + y^4 = (5 + √35)^4 + (-5 + √35)^4
= 14200