（3a-b+c）（3a-b-c）+（3a+b）²
=[3a+(b+c)][3a-(b+c)]+（3a+b）²
=9a²-(b-c)²+（3a+b）²
=9a²-b²+2bc-c²+9a²+6ab+b²
=18a²-c²+6ab+2bc
（a-m+n）²
=[(a-m)+n]^2
=(a-m)^2+2n(a-m)+n^2
=a^2-2am+m^2+2an-2mn+n^2