Learn and practice essential geometry skills. The answer to every problem, along with helpful notes, can be found at the back of the book. This volume focuses on fundamental concepts relating to triangles, and also covers quadrilaterals and other polygons. Topics include: lines, angles, and transversals - angles of a triangle - congruent triangles - similar triangles and ratios - right triangles, including the Pythagorean theorem and special triangles - perimeter and area of a triangle, including Heron’s formula - thorough coverage of bisectors, medians, and altitudes, including the incenter, circumcenter, centroid, and orthocenter (though the concepts of inscribed or circumscribed circles are reserved for Volume 2) - the triangle inequality - quadrilaterals - polygons The author, Chris McMullen, Ph.D., has over twenty years of experience teaching math skills to physics students. He prepared this workbook of the Improve Your Math Fluency series to share his strategies for solving geometry problems and formulating proofs. What exactly is plane geometry? It is the same as ordinary geometry, except that it is focused on figures that can be drawn within the plane, like polygons (the focus of Volume 1) and circles (the focus of Volume 2). The title of this book could easily have been "Geometry Practice Workbook with Answers" instead of "Plane Geometry Practice Workbook with Answers" (but including the word "plane" is more precise). Which topics are included in this book? Volume 1 covers lines, angles, transversals, complementary/supplementary angles, vertical angles, triangles, the angle sum theorem, congruence tests, similarity tests, right triangles, the Pythagorean theorem, special triangles, perimeter, area, Heron's formula, medians, bisectors, altitudes, the triangle inequality, quadrilaterals, and polygons. Significant attention is given to medians, bisectors, altitudes, quadrilaterals, and polygons. Volume 2 (sold separately) covers circles, including radius, diameter, circumference, area, central angles, arc length, degrees/radians, inscribed angles, Thales's theorem, chords, circular segments, secants, tangents, and inscribed/circumscribed shapes. The final chapter goes beyond the plane to explore common 3D shapes, including the cube, prism, pyramid, polyhedra, sphere, cylinder, and cone. Significant attention is given to inscribed/circumscribed shapes and to the chapter on 3D shapes. What qualifications and experience does the author have? Chris McMullen earned a Ph.D. in physics from Oklahoma State University and has over 20 years of experience teaching university physics. Geometry concepts come up in a wide variety of physics problems. The author has published several papers on the collider physics of extra dimensions of spacetime in physics journals, which involves higher-dimensional geometry. Chris McMullen is also the author of popular science books on the geometry of a fourth dimension of space (Extra Dimensions, Volumes 1-2). Which kinds of problems are included? Plenty of problems ask the student to solve for something for which they can find a numerical answer (by applying ideas learned in the book). Occasional problems ask the student to prove an important theorem or to derive an important formula. There are a few other kinds or problems, too. Examples in the book should serve as a handy guide. Answers and notes are included at the back of the book.