b) x8 +7x4+16
= x8+8x4-x4+16
= (x8+8x4+16) - x4
=(x4+4)2-x4
= (x4+4+x2)(x4+4-x2)
c) x5+x-1
= x5 - x4+x3+x4-x3+x2-x2+x-1
= x3(x2-x+1) + x2(x2-x+1) - (x2-x+1)
= (x2-x+1)(x3+x2 -1)
d)x7+x2+1
=x7-x+x2 +x+1
= x (x6-1) + (x2+x+1)
= x(x3-1)(x3+1) + (x2+x+1)
= x(x3+1)(x-1)(x2+x+1)+(x2+x+1)
= (x2+x+1)[x(x3+1)(x-1) +1]
= (x2+x+1)(x5-x4+x2-x+1)
= x (x-1)(x2+x+1)
e) x5+x4+1
= x5+x4+x3 - x3+1
= x3(x2+x+1) - (x-1)(x2+x+1)
= (x2+x+1)(x3-x+1)
f) x8+x+1
= x8-x2+x2+x+1
= x2(x6-1)+(x2+x+1)
= x2(x3-1)(x3+1) +(x2+x+1)
= (x5+x2)(x-1)(x2+x+1) +(x2+x+1)
= (x2+x+1)(x6-x5+x3-x2+1)
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