Lines of SymmetryDate: 03/17/97 at 20:19:46 From: Dennis Dziadus Subject: Lines of Symmetry What are lines of symmetry? Date: 03/18/97 at 14:00:18 From: Doctor Rob Subject: Re: Lines of Symmetry A line of symmetry is an imaginary line drawn through a plane figure such that if the figure is flipped over using that line as an axis of rotation, you get the same figure back again. A simple example is an isosceles triangle. Suppose that you orient the figure so that the odd side (length not equal to the other two, which are equal to each other) is horizontal, and the opposite vertex is above it. Then the line of symmetry is the altitude from that vertex down to that odd side. It is not part of the original figure, which is why I called it imaginary, but it is easy to construct. If you flip the triangle over using this altitude as an axis of rotation, the equal sides will be swapped, the equal base angles will be swapped, the vertex angle will be left alone, and the base will be left in place. You will get an identical copy of the original figure. Another, more complicated example is a square. There are four lines of symmetry. Two are the diagonals of the square, and two are the perpendicular bisectors of the sides. Can you see why? These lines are not part of the original figure, but are constructed from it. If you need more explanation, write again and we'll try harder. -Doctor Rob, The Math Forum Check out our web site! http://mathforum.org/dr.math/ |
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