[질문] 개념플러스유형9가 48쪽 49쪽 답

ac,ad,bc,bd//a,b,a,b,b//3x^2-3xy,2x^2-3x-9,6a^2+7ab-5b^2,3x^2-8xy-4y^2+8y//5x^2+5xy-20x,ab+7a-3b-21,16x^2-9,2x^2-xy-y^2+2x+y//5