A={x∈N,x2−10x+9≤0} ={1,2,3,...,9} B={1,4,9,16,......} f(x)≤(x−3)2+1 f(1)≤5,f(2)≤2,..........f(9)≤37 x=1 has 2 choices x=2 has 1 choice x=3 has 1 choice x=4 has 1 choice x=5 has 2 choices x=6 has 3 choices x=7 has 4 choices x=8 has 5 choices x=9 has 6 choices ∴ Total functions =2×1×1×1×2×3×4×5×6=1440