(1+2x+x²)²
=(1+2x+x²)(1+2x+x²)
=1×(1+2x+x²)+2x×(1+2x+x²)+ x²×(1+2x+x²) (分配率)
=(1+2x+x²)+(2x+4x²+2x³)+(x²+2x³+x^4) (分配率)
=1+4x+6x²+4x³+x^4