(1)a2-8a+12=a2-8a+16-16+12=(a-4)2-22=(a-4+2)(a-4-2)=(a-2)(a-6);(2)a2+4ab+3b2=a2+4ab+(2b)2+3b2-(2b)2=(a+2b)2-b2=(a+2b+b)(a+2b-b)=(a+3b)(a+b).