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: 8

Answer

(a) Vertex: $V(h,k)=V(-3,-2)$ Focus: $F(-3,-7)$ Directrix: $y=3$

Work Step by Step

Equation of a parabola with vertical axis and vertex at $(h,k)$: $(x-h)^2=4p(y-k)$ $(x+3)^2=-20(y+2)$ $[x-(-3)]^2=-20[y-(-2)]$ $h=-3$ $k=-2$ Vertex: $V(h,k)=V(-3,-2)$ $4p=-20$ $p=-5$ The given equation can be obtained by shifting $x^2=-20y$ legft 3 units and downward 2 units. In this equation: Focus: $F(0,p)=F(0,-5)$ Directrix: $y=-p=5$ Now, shift the focus and the directrix 3 units to the left and 2 units downward: Focus: $F(-3,-7)$ Directrix: $y=3$
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