A={x|x^2-3x+2=0}
={x| (x-1)(x-2) = 0}
= {1,2}
A∪B = A => B is subset of A
B={x|x^2-ax+2=0}
for x=1
1-a + 2 = 0
a = 3
for x=2
4-2a+2=0
a = 3
ie a =3 #