\(f\left(8\right)=a.8^2+b.8+c=64a+8b+c=8\left(5a+b\right)+24a+c=24a+c\)
\(f\left(-3\right)=a.\left(-3\right)^2+b.\left(-3\right)+c=9a-3b+c=-3\left(5a+b\right)+24a+c=24a+c\)
\(f\left(8\right).f\left(-3\right)=\left(24a+c\right).\left(24a+c\right)=\left(24a+c\right)^2\ge0\forall a,b,c\)
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f(8)=a.82+b.8+c=64a+8b+c=8(5a+b)+24a+c=24a+cf(8)=a.82+b.8+c=64a+8b+c=8(5a+b)+24a+c=24a+c
f(−3)=a.(−3)2+b.(−3)+c=9a−3b+c=−3(5a+b)+24a+c=24a+cf(−3)=a.(−3)2+b.(−3)+c=9a−3b+c=−3(5a+b)+24a+c=24a+c
f(8).f(−3)=(24a+c).(24a+c)=(24a+c)2≥0∀a,b,c
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