Question

设集合A={x,x的平方-3x+2=0},B={x,x的平方-ax+2},若A并B=A,求a的取值范围

Answer 1

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 #