if one zero of polynomial q(x)=x^2+px+8 is double the other then find the value of p.

Let the zeroes be a and b..
then we know the general form of quadratic equation as:
k{x²-(a+b)x+ab}
​comparing this general equation with the given polynomial (x²+px+8) we get,
a+b=p - (i) and
ab = 8 - (ii)
also it is given that a = 2b - (iii)
on putting the value of a = 2b in eqn. (ii) we get,
(2b)b=8
2b²=8
b²  = 8/2=4
b = 2
putting the value b = 2 in equation 3 we get,
a = 4
on putting the values of a and b in equation 1. we get,
p= 2+4 = 6
so the value of p is 6