Solve the quadratic equation by completing the square: `k^2-12k-21 = 19` 

Box 1: Enter your answer as a list of values separated by commas: Example: -4, 3, 2
Enter each value as a number (like 5, -3, 2.2172) or as a calculation (like 5/3, 2^3, 5+4)
Enter DNE for Does Not Exist, oo for Infinity
Decimal values are not allowed