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d=var('d') d is integer and d>4

f(d)=1/6(d^2 - sqrt(d^2 + 8d - 8)d + 23d - sqrt(d^2 + 8d - 8) - 26)(d - sqrt(d^2 + 8*d - 8) + 4)/(d + 1)

How can I show that f(d)>=0

bool(f(d)>=0) and bool(f(d)<0) return false

d=var('d') d d=var('d') $d$ is integer and d>4$d>4$

f(d)=1/6*(d^2 - sqrt(d^2 + 8d 8*d - 8)d 8)*d + 23d 23*d - sqrt(d^2 + 8d 8*d - 8) - 26)(d 26)*(d - sqrt(d^2 + 8*d - 8) + 4)/(d + 1)
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