Distance d between two points P(a,b) and Q(c,d) is given by,
d=√(a−c)2+(b−d)2
Given that :
P(am21,2am1)
Q(am22,2am2)
Now apply the above given formula,
d=√(am21−am22)2+(2am1−2am2)2
d=a√(m21−m22)2+(2m1−2m2)2
d=a√[(m1+m2)(m1−m2)]2+4(m1−m2)2
Taking (m1−m2)2 common we get,
⇒d=a(m1−m2)√(m1+m2)2+4