Shapes of Budget Constraints - Quantity Discounts

Suppose p2 is constant at $1 but that p1=$2 for 0 £ x1 £ 20 and p1=$1 for x1ᡌ. Then the constraint’s slope is - 2, for 0 £ x1 £ 20-p1/p2 = - 1, for x1 > 20and the constraint is

Suppose p2 is constant at $1 but that p1=$2 for 0 £ x1 £ 20 and p1=$1 for x1ᡌ. Then the constraint’s slope is - 2, for 0 £ x1 £ 20 -p1/p2 = - 1, for x1 > 20 and the constraint is