using binomial theorem ,expand:(1-x+x2)4

    1-x+x24=1-x+x24=C041-x4+C141-x3x2+C241-x2x4+C341-x1x6+C44x8=1-x4+4x21-x3+6x41-x2+4x61-x+x8=C04-C14x+C24x2-C34x3+C44x4+4x2C03-C13x+C23x2-C33x3+6x41-2x+x2+4x61-x+x8=1-4x+6x2-4x3+x4+4x21-3x+3x2-x3+6x41-2x+x2+4x61-x+x8=1-4x+6x2-4x3+x4+4x2-12x3+12x4-4x5+6x4-12x5+6x6+4x6-4x7+x8=1-4x+10x2-16x3+19x4-16x5+10x6-4x7+x8

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