Algebra and Trigonometry 10th Edition

Published by Cengage Learning
ISBN 10: 9781337271172
ISBN 13: 978-1-33727-117-2

Chapter 1 - 1.1 - Graphs of Equations - 1.1 Exercises - Page 79: 40

Answer

There is no symmetry about the x-axis, y-axis nor the origin. See graph The intercepts: $(-2,0)$, $(0,0)$, $(0,0)$.

Work Step by Step

$$y=-x^2-2x$$ Testing for x-symmetry: $$y=-(-x)^2-2(-x)$$ $$y=-x^2+2x$$ Since the resulting equation is not the same as the original equation, there is no x-symmetry. Testing for y-symmetry: $$-y=-x^2-2x$$ $$y=x^2+2x$$ Since the resulting equation is not the same as the original equation, there is no y-symmetry. Testing for origin-symmetry: $$-y=-(-x)^2-2(-x)$$ $$-y=-x^2+2x$$ $$y=x^2-2x$$ Since the resulting equation is not the same as the original equation, there is no origin-symmetry. Rewriting the equation in vertex form: $$-y=x^2+2x$$ $$-y+(\frac{-2}{2})^2=x^2+2x+(\frac{-2}{2})^2$$ $$-y+1=x^2+2x+1$$ $$-(y-1)=(x+1)^2$$ $$y-1=-(x+1)^2$$ Thus, the vertex is at $(-1,1)$. Finding the x-intercepts: $$0=-x^2-2x$$ $$0=-x(x+2)$$ $$0=x(x+2)$$ $$x=0$$ $$x+2=0$$ $$x=-2$$ Thus, the x-intercepts are $(-2,0)$ and $(0,0)$. Using the points, the graph is as shown. The intercepts are as for x-intercepts $(-2,0)$ and $(0,0)$, and for y-intercept $(0,0)$.
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