standard_description: Prove the slope criteria for parallel and perpendicular lines and use them to solve geometric problems (e.g., find the equation of a line parallel or perpendicular to a given line that passes through a given point).
problem_activity: Problem 1
Sondra says
$$3\times223=696$$
. Use what you know about the product of two odd numbers to explain why Sondra is wrong.
Problem 2
Explain two ways you could find the next number in the highlighted diagonal below. You don’t need to actually compute it!
| **            ×           **  | **            1           ** | **            2           ** | **            3           ** | **            4           ** | **            5           ** | **            6           ** | **            7           ** | **            8           ** | **            9           ** | **            10           ** |   |
|-------------------------------|------------------------------|------------------------------|------------------------------|------------------------------|------------------------------|------------------------------|------------------------------|------------------------------|------------------------------|-------------------------------|---|
| **            1           **  |              1               |              2               |              3               |              4               |              5               |              6               |              7               |              8               |              9               |              10               |   |
| **            2           **  |              2               |              4               |              6               |              8               |              10              |              12              |              14              |              16              |              18              |              20               |   |
| **            3           **  |              3               |              6               |              9               |              12              |              15              |              18              |              21              |              24              |              27              |              30               |   |
| **            4           **  |              4               |              8               |              12              |              16              |              20              |              24              |              28              |              32              |              36              |              40               |   |
| **            5           **  |              5               |              10              |              15              |              20              |              25              |              30              |              35              |              40              |              45              |              50               |   |
| **            6           **  |              6               |              12              |              18              |              24              |              30              |              36              |              42              |              48              |              54              |              60               |   |
| **            7           **  |              7               |              14              |              21              |              28              |              35              |              42              |              49              |              56              |              63              |              70               |   |
| **            8           **  |              8               |              16              |              24              |              32              |              40              |              48              |              56              |              64              |              72              |              80               |   |
| **            9           **  |              9               |              18              |              27              |              36              |              45              |              54              |              63              |              72              |              81              |              90               |   |
| **            10           ** |              10              |              20              |              30              |              40              |              50              |              60              |              70              |              80              |              90              |              100              |   |
|                               |                              |                              |                              |                              |                              |                              |                              |                              |                              |                               |   |


aligns: no