At about the 1:23 mark (and he continues the mistake further in the problem), the teacher writes 3x+8 on the board instead of 3x+9. The teacher does the rest of the work correctly, but because of this error, he gets the wrong answer. He should get x=23 and measure of angle LKM=156.
In this lesson, we learn about angle bisectors and how to use them to solve for unknown angles. By understanding that bisecting an angle cuts it in half, we can use this knowledge to find missing angles by setting them equal to each other. Through practice problems, we see how to use supplementary angles and solve for x to find the measure of an angle. This lesson is a great introduction to using geometry to solve for unknowns.
Using angle bisectors and supplementary angles to solve for x
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Questions answered by this video:
What does angle bisector mean?
How can I solve for an angle measure when I know I have an angle bisector?
How do I solve for the measure of the angle when I the angle measure I am given has a variable in it?
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This lesson shows how to solve for an angle measure when you are given the angle measure with a variable in it, and you know that you have an angle bisector.