An algebra tile configuration. Only the Product spot is shown. 8 tiles are in the Product spot in 4 columns with 4 rows. First row: 1 + x squared, 3 negative x. Second row: 1 negative x, 1 +. Third and fourth rows: 1 negative x.
How many more unit tiles must be added to the function f(x)=x2−6x+1 in order to complete the square?
1
6
8
9