x(x−2009)−y(2009−x)=x(x−2009)+y(x−2009)=(x−2009)(x+y)Thay−vao(3009−2009)(3009+1991)=1000.5000=5000000
x2−y2−2x+2y=(x+y)(x−y)−(2x−2y)=(x+y)(x−y)−2(x−y)=(x−y)(x+y+2)Thay−vao=(2345−2344)(2345+2344+2)=1.4691=4691
Câu c coi lại đề chút, phải là:
x2+2009x−y2+2009y
PS: Hãy like khi mk đã giúp đỡ bn