[Siren-Of-Step]

ข้อ 40
เราจะได้ว่า$ (x-5)(x-3y)(x-y) = x^3-ax^2 + 52x -b = 0$
$4y +5 = a$
$3y^2 +20y = 52 \Leftrightarrow y = 2$
$15y^2=b$
ทำได้ $b= 60 , a = 13 , a+b = 73$