It is quick and easy to check your angle measures when working with complementary, supplementary and triangle measures. After your find your missing angle, you simple add it to the other angles and make sure you get a sum of 90 for complementary angles and 180 for supplementary angles and all three angles of a triangle. Checking your work in math is crucial. For, you may understand the concept perfectly and make a minor computation error and go from an A answer to an F in an instant. Here are some examples of how to check your work to ensure those good grades:
Check your work for complementary angles:
EXAMPLE 1: If angle A = 70°, then B = 20°
Check it, 70 + 20 = 90°. CORRECT, the sum of complementary angles is always 90°!
EXAMPLE 2: If angle A = 45°, then B = 55°
Check it, 45 + 55 = 100. INCORRECT, the sum needs to be 90!!! Fix it before moving on.
Check your work for supplementary angles:
EXAMPLE 1: If angle A = 130°, then B = 50°
Check it, 130 + 50 = 180. CORRECT, the sum of supplementary angles is always 180°!
EXAMPLE 2: If angle A = 162°, then B = 22°
Check it, 162 + 22 = 184. INCORRECT, the sum should be 180. A common mistake was made, forgetting to borrow with subtraction, but it’s not to let to fix it.
Check your work for the missing angle of a triangle:
EXAMPLE 1: If angle A = 90°, B = 50°, then C = 40°
Check it, 90 + 50 + 40 = 180°. CORRECT, all three angles of a triangle have the sum of 180°!
EXAMPLE 2: If angle A = 53°, B = 33°, then C = 9
Check it, 53 + 33 + 9 = 98. INCORRECT, the sum should be 180, not 98. Forgetting to borrow with subtraction is a common error that affects the math grades of many 6th graders. This can be avoided by simply using addition to check the final sum.