If x=8 what is the value of x(17-x)?

The highest power is 2.
Explanation:
Because x has a maximum power of 2, there will be 2 answers. if it were 3, there could be up to 3 answers, etc.
While solving this problem, you gather all terms on one side so the equation looks like
x
2
−
81
+
17
=
0
x
2
−
64
=
0
then factor
(
x
−
8
)
(
x
+
8
)
=
0
then, because any number times 0 equals 0, we know that one of the two parts in the parenthesis must be equal to 0, so
x
−
8
=
0
or
x
+
8
=
0
and so the two answers
x
=
8
,
−
8
come to be.