Precalculus: Mathematics for Calculus, 7th Edition

Published by Brooks Cole
ISBN 10: 1305071751
ISBN 13: 978-1-30507-175-9

Chapter 11 - Review - Exercises - Page 833: 11

Answer

(a) Vertex: $V(-2,-3)$ Focus: $F(-2,-2)$ Directrix: $y=-4$ (b)

Work Step by Step

Equation of a parabola with vertical axis and vertex at $(h,k)$: $(x-h)^2=4p(y-k)$ $\frac{1}{2}x^2+2x=2y+4$ $\frac{1}{2}x^2+2x+2=2y+4+2$ $\frac{1}{2}(x+2)^2=2(y+3)$ $[x-(-2)]^2=4[y-(-3)]$ $h=-2$ $k=-3$ Vertex: $V(h,k)=V(-2,-3)$ $4p=4$ $p=1$ The given equation can be obtained by shifting $x^2=4y$ left 2 units and downward 3 units. In this equation: Focus: $F(0,p)=F(0,1)$ Directrix: $y=-p=-1$ Now, shift the focus and the directrix 2 units to the left and 3 units downward: Focus: $F(-2,-2)$ Directrix: $y=-4$
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