Maths唔識抵死題 (probability)

Q1 First find out the probability that none of the people were born on the same day. The probability is (365/365)(364/365)(363/365)(362/365)(361/365)=0.9729

So, since at least two of them were born on the same day is just the complement of the above event. The required probability is 1-0.9729=0.027

Q2 By the relationships between roots and coefficients,
A+B=-4/2=-2 and AB=k/2

A^2+B^2=6
(A+B)^2-2AB=6
(-2)^2-2(k/2)=6
4-k=6
k=-2

2010-12-26 15:27:03 補充：
用根與係數的關係。ax^2+bx+c=0的根是x,y
x+y=-b/a,
xy=c/a

for Q2, explain more the first step....

2010-12-28 19:45:38 補充：
sorry, i still son't understand Q2... explain more