x
=
−
8
,
−
2
Explanation:
Given:
x
2
+
10
x
+
16
=
0
To complete the square put the two
x
terms on the left and the constant on the right of the equation:
x
2
+
10
x
=
−
16
Complete the square by multiplying the
x
-term by
1
2
:
1
2
⋅
10
=
5
and adding the square of this number to the right side of the equation:
5
2
=
25
(
x
+
5
)
2
=
−
16
+
25
UNDERSTANDING CHECK:
(
x
+
5
)
2
=
x
2
+
10
x
+
25
.
The
+
25
was not in the original equation. If we add
+
25
to one side of the equation, we must add the same amount to the other side of the equation to keep it balanced.
(
x
+
5
)
2
=
9
To solve, square root both sides of the equation:
√
(
x
+
5
)
2
=
±
√
9
x
+
5
=
±
3
x
=
−
5
±
3
x
=
−
5
+
3
=
−
2
,
x
=
−
5
−
3
=
−
8
x
=
−
8
,
−
2
