Answer:
The simplified form of given expression is
.
Step-by-step explanation:
The given expression is

Here, we have to factors (x-3) and (x+7).
Factor (x-3) has two terms x and -3. Write these terms in first row.
Factor (x+7) has two terms x and 7. Write these terms in first column.
Now, find the elements of the table by multiplying corresponding rows and columns.
The elements of the table are x², -3x, 7x, -21.
Now, add all these elements.

Therefore the simplified form of given expression is
.