Geometry: Common Core (15th Edition)

Published by Prentice Hall
ISBN 10: 0133281159
ISBN 13: 978-0-13328-115-6

Chapter 3 - Parallel and Perpendicular Lines - 3-5 Parallel Lines and Triangles - Practice and Problem-Solving Exercises - Page 175: 11


$m∠1$ = $90^{\circ}$

Work Step by Step

The measures of the three angles of a triangle equal $180^{\circ}$; therefore, if we have the measure of the other two angles, we can figure out the measure of $∠1$. Let $x$ equal $m∠1$: $33 + 57 + x = 180$ Add the constants on the left side together: $90 + x = 180$ Subtract $90$ from each side to solve for $x$: $x = 90$ $m∠1$ = $90^{\circ}$
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