bai nay truoc het ta chu y . cac sô duoi can co the phan tich thanh binh phuong dung
(dau can minh viet thanh dau / nha)
nhân C lên 2 ta co
/2*/(2+/3)=/(4+2/3)=/(3+2/3+1)=/(/3+/1)^2=/3+1
tuong tu
2C=21(/3+1+/5-1)^2-6(/3-1+/5-1)^2-30/15
=21(/3+/5)^2-6(/3+/5)^2-30/15
=15(/3+/5)^2-30/15
=45+75+30/15-30/15
=120
co cho nao chua hieu thi cau co the hoi to