1. Let a coordinate be (m, n), then, according to OB=4AB, m=4n, and then according to the area calculation formula 1/2(m*n)= 1/2, m*n= 1, then we This is the coordinate of a, and the return function 1/2=k/2. You can know that k= 1.

This is a decreasing function. If x1>; X2, then y 1

3. The minimum value is twice that of the line segment OP. The minimum value of OP is when the coordinate of P is (1, 1), that is, the length of OP is (root number 2), so the minimum value of PQ is "2 times (root number 2)".