Đáp án:a, x7+x2+1=(x7 – x) + (x2 + x + 1)
= x.(x6 – 1) + (x2 + x +1)
= x.(x3 - 1).(x3 +1) + (x2 + x +1)
= x.(x-1).(x2 + x +1).(x3 +1) + (x2 + x +1)
= (x2 + x +1).[x.(x-1).(x3 +1) + 1]
= (x2 + x +1).[(x2-x).(x3 +1) + 1]
= (x2 + x +1).(x5-x4 + x2 -x + 1)
b,x10+x5+1
=x10+x5+1+x2-x-x
=(x10-x)+(x5-2)+(x2+x+1)
=x(x9)-1+x2 (x3-1)+(x2+x+1)
=x(x6+x3+1)(x3-1)+x2(x-1)(x2+x+1)+(x2+x+1)
=(x7+x4+x) (x2+x+1) (x-1)+(x3-x2)(x2+x+1)+(x2+x+1)
=(x2+x+1)(x8-x7-x5-x4-x2-x-x3-x2+1)
=(x2+x+1)(x8-x7-x5-x4-x-x3+1)
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