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# Equation practice with vertical angles

Given algebraic expressions that represent a pair of vertical angles, Sal forms and solves an equation. Created by Sal Khan.

## Want to join the conversation?

• Can you give me a summary of this video vertical angles is a very ambiguous concept.
• In this lesson the vertical angles part isn't important. Sal uses vertical angles as an application of a question like the ones he demonstrated in the video. Here is an example:

9x+72=4x+112
(9x+72)-4x=(4x+112)-4x
5x+72=112
Here we will "switch" the numbers around and combine like terms
5x=112-72
5x=40
x=8 degrees
Hope this helps.
• Are vertical angles complementary or supplementary or does it depend on the degrees in the question?
• Vertical angles are basically another word for opposite angles. If one of the vertical angles is 90° then the other one has to be 90° This would make it supplementary, because if both of the angles are 90 degrees they add up to 180°. The same thing goes for the complementary angles, because there is only one way to represent them. Since vertical angles have the same measure on their mirrored side, there is no other way to make 90° aside from 45° and 45°. This meaning that 31° and 59° degrees would not work. ( This is the same for the supplementary angles ) So yes, the vertical angles could either be supplementary, complementary, or something else ( such as 67° and 67° are vertical angles, yet they are not supplementary or complementary because they don't add up to either 90° or 180°. So your answer could be yes, meaning that they could be both, but your answer also could be no, because there are many different ways, such as my example, which adds up to 134°, meaning that it is not supplementary or complementary. Hopefully you found this useful (also sorry if it was too long)
• Is it just me or does it seem that everybody's post gets a vote as soon as you post it?
• FR tho
• What if their is a vertical angle. But one is 3x and the other is (80-x)? How would you solve that?
• If the angles are vertical, then they are congruent, or the same measure. Therefore, if a vertical equals 3x and the other equals 80-x, you would simply set up an equation: 3x equals 80-x. add x to both sides, then you would get 4x equals 80. Solve for x, and you get x equals 20. I hope this helps you!
• how do I know what to subtract off of? for example: Sal subtracted 7x off on both sides. does that mean you take the smaller of the numbers beside the x to subtract, or does that mean you just take the one on the right to subtract?
• He's constraining the variables by 'cancelling', using legitimate operations and following the addition rule of equalities. He happened to cancel 7x, but could have chosen anything else as long as it constrains the variable to the form variable = number. https://youtu.be/vA-55wZtLeE https://youtu.be/f15zA0PhSek
• Can someone please assist me? I am having trouble making sense of this.
• Hello, but could you specify what you are confused about? I just need to know what is confusing you to help you.
(1 vote)
• On my worksheet, it has a problem that does not contain numbers. It is just two lines in a x shape, then y over 4, x, y, and y in each spot. Then it says to find out what x and y are. Pls help! I am in the 6th grade gifted program and in fast math, if that helps
• y and y are obviously vertical angles. That means that the remaining two angles: x and y/4 must be vertical angles. Therefore:
y = y (duh)
x = y/4 (little more helpful)
the first equation: y = y won't help us since we need a system with with two variables in each equation. Remember that angles on the same line are supplementary:
y + x = 180
Now we can solve the system:
x = y/4
y + x = 180
y + y/4 = 180
5y/4 = 180
5y = 520
y = 104deg
104 + x = 180
x = 76deg
• when setting up the equation, does it matter which piece goes first? Because sometimes I would do the problem, and it would come out the opposite of the correct answer.
• Hey fellows, does it matter if we put 7x+182 at first and 9x+194 at last?

Like this----- 7x+182 = 9x+194