真惱羞成怒
2023-04-24 14:08:37
16a) x^2 + ax + b = 0 have root p and 5p
Show 5a^2 = 36b
16b)
y = mx meet C at P and Q
Circle equation C: x^2 +y^2 -12x -6y + 20 =0
Sub y = mx in, we have
(m^2+1) x^2 - (6m+12)x + 20 = 0
x^2 - (6m+12)x /(m^2+1) + 20/(m^2+1) = 0 --(1)
Let x coordinate of P and Q be a and b
OP : PQ = 1 : 4 ==> a : b = 1 : 5
Note a and b are roots of (1)
Using (a) we have 5[(6m+12)/(m^2+1)]^2 = 36 (20) / (m^2+1)
Solving m = 4/3 or 0