原式=(x+(a+b))^2-(a+b)^2-3a^2+10ab-3b^2
=(x+(a+b))^2-(4a^2-8ab+4b^2)=(x+(a+b))^2-4(a^2-2ab+b^2)
=(x+(a+b))^2-(2(a-b))^2
=(x+(a+b)-2(a-b))*(x+(a+b)+2(a-b))
=(x+3b-a)*(x+3a-b)