Question

已知x∈R,y∈N*,A={y|y=x2-4x+6},B={y|y=-x2-2x+18},求A∩B

求答案啊

Answer 1

A={y|y=x²-4x+6}
y=x²-4x+6=(x-2)²+2≥2

B={y|y=-x²-2x+18}
y=-x²-2x+18=-(x+1)²+19≤19

A∩B={y|2≤y≤19且y∈N*}

Answer 2

A:y=(x-2)^2+2
y≥2 y∈N+

B：y=-x^2-2x+18
=-(x+1)^2+19
y≤19 y∈N+

A∩B={y∈N+|2≤y≤19}