xpand by using Binomial theorem (5-x)^6
(5−x)6=[(−1)⋅(x−5)]6=(−1)6⋅(x−5)6|(−1)6=1=(x−5)6
(x−5)6=(60)x6⋅50−(61)x5⋅51+(62)x4⋅52−(63)x3⋅53+(64)x2⋅54−(65)x1⋅55+(66)x0⋅56=(60)x6−51⋅(61)x5+52⋅(62)x4−53⋅(63)x3+54⋅(64)x2−55⋅(65)x1+56⋅(66)(60)=(66)=1(61)=(65)=6(62)=(64)=15(63)=20=1⋅x6−51⋅6⋅x5+52⋅15⋅x4−53⋅20⋅x3+54⋅15⋅x2−55⋅6⋅x1+56⋅1=x6−30 x5+375 x4−2500 x3+9375 x2−18750 x+15625