a²+2ab+b²-2ac-2bc+c²=a²+2ab+b²-[2ac+2bc]+c²
=(a+b)²-[a²+2ac+c²-a²-c²+b²+2bc+c²-b²-c²]+c²
=(a+b)²-[(a+c)²-a²-c²+(c+b)²-b²-c²]+c²
=(m+3)²-[(m+4)²-a²-c²+(m+5)²-b²-c²]+c²
=(m+3)²-(m+4)²+a²+c²-(m+5)²+b²+c²+c²
=(m+3)²-(m+4)²-(m+5)²+a²+b²+3c²
=(m+3+m+4)(m+3-m-4)-(m+5)²+a²+b²+3c²
=-2m-7-(m+5)²+(1/2m+1)²+(1/2m+2)²+3(1/2m+3)²
=-2m-7-m²-10m-25+1/4m²+m+1+1/4m²+2m+4+3/4m²+9m+27
=1/4m²+2m+7