Answers and Explanations 153
Answers
1–100
69.
y
x
=
+
−
3
2
2
4
2
(
)
The vertex form of a parabola is given by y = a(x – h)
2
+ k, with the vertex at the point
(h, k). Using the vertex (–2, –4) gives you the following equation:
y a x
a x
=
− −
(
) −
=
+
−
( )
(
)
2
4
2
4
2
2
Now use the point (0, 2) to solve for a:
2
0 2
4
2 4
4
6 4
3
2
2
=
+
−
=
−
=
=
a
a
a
a
(
)
Therefore, the equation of the parabola is
y
x
=
+
−
3
2
2
4
2
(
)
70.
y = –(x + 1)
2
+ 6
The vertex form of a parabola is given by y = a(x – h)
2
+ k, with the vertex at the point
(h, k). Using the vertex (–1, 6), you have the following equation:
y a x
a x
=
− −
(
) +
=
+
+
( )
(
)
1
6
1
6
2
2
Now use the point (1, 2) to solve for a:
2
1 1
6
2 4
6
4 4
1
2
=
+
+
=
+
− =
− =
a
a
a
a
(
)
Therefore, the vertex form of the parabola is
y
x
= − +
+
(
)
1
6
2