Question

cho a b c d l

 

Answer 1

a/a+b +b/b+c +c/a+d +d/d+a=2
suy ra (a/a+b +c/c+d -1)+(b/b+c +d/d+a -1)=0
=ac-bd/(a+b)(c+d) - ca-bd/(b+c)(d+a)=0
=(ac-bd).(1/(a+b)(c+d) - 1/(a+d)(b+c))=0
=(ac-bd).(ab+ac+bd+dc-ac-ad-bc-bd)/(a+b)(b+c)(c+d)(d+a)=0
=(ac-bd).(ab+cd-ad-bc)=0
=(ac-bd)(a-c)(b-d)
vì a#b#c#d nên a-c#0, b-d#0 suy ra ac-bd=0
suy ra ac-bd suyy ra ac.bd=(bd)^2

Answer 2

doan cuoi thi sao no la cac so chinh phuong vay ban