Question 9
Let a,b,c,d be root of x^4 - 8x^3+21x^2-20x+5=0 where a+b=c+d
So using sum of roots a+b+c+d = 8, so a+b = c+d = 4
From product of roots abcd = 5 .....(1)
From sum of roots 2 at a time:
ab +cd +ac+ad+bc+bd = 21
ab+cd + a(c+d) +b(c+d) =21
ab+cd+(a+b)(c+d) = 21
Since a+b =...