For set A
(x2−10x+9)≤0⇒(x−1)(x−9)≤0
⇒x∈[1,9]
i.e. A=1,2,3,4,5,6,7,8,9
Given B=n2:n∈N
Now f(x)≤(x−3)2+1
For x=1:f(1)≤5⇒B∈12,22
For x=2:f(2)≤2⇒B∈12
For x=3:f(3)≤1⇒B∈12
For x=4:f(4)≤2⇒B∈12
For x=5:f(5)≤5⇒B∈12,22
For x=6:f(6)≤10⇒B∈12,22,32
For x=7:f(7)≤17⇒B∈12,22,32,42
For x=8:f(8)≤26⇒B∈12,22,32,42,52
For x=9:f(9)≤37⇒B∈12,22,32,42,52,62
Total number of such function
=2×1×1×1×2×3×4×5×6=2(720)=1440