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Addition Equations will make several elements of geometry a SNAP! When you were in the 5th grade, your teacher made you learn 3 or 4 formulas for every geometric calculation. Now, with your algebra skills you need to learn only 1!
OK
For example: Complimentary Angles create a right angle. So Angle1 (A1) + Angle2 (A2) = 90. Which equation will you use to find Angle2?
A1 + 45 = 90
45 + A2 = 90
90 + 45 = A2
Let's try it for real! One of a pair of complimentary angles measures 60o. What is the measure of the other angle?
30o
Supplementary Angles create a straight angle. So Angle1 (A1) + Angle2 (A2) = 180. Which equation will you use to find Angle2?
A1 + 75 = 180
75 + A2 = 180
180 + 75 = A2
Let's try it for real! One of a pair of supplementary angles measures 110o. What is the measure of the other angle?
70o
The sum of the measures of the interior angles of a triangle will equal 180o So Angle1 (A1) + Angle2 (A2) + Angle3 (A3) = 180. Which equation will you use to find Angle2?
A1 + 75 + 45 = 180
75 + A2 + 45 = 180
180 + 75 + 45 = A2
Let's try it for real! Melissa drew an isosceles triangle with a pair of angles measuring 50o. What is the measure of the third angle?
80o
Notice how much easier geometry becomes, now that you know a little algebra. With solving addition equations, you can do all of these angle calculations as well as perimeter problems. The perimeter of a quadrilateral is 120 feet. If the sum of 3 sides is 100 feet, what is the measure of the 4th side?
20 feet
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