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# Congruence and similarity — Harder example

Watch Sal work through a harder Congruence and similarity problem.

## Want to join the conversation?

• Sal puts easy videos in harder cases....lol
• Great now how do I do it in a minute :/
• by doing it in 20 seconds
• how is this the harder example
• These type of question are normally easy for people.
• how do we know if the two lines are parallel?
• to make it simpler, in the school hall you and your friend walk beside each other to go to class, you are parallel/ next to each other without ever becoming each other or being in the exact same place at the same time
• What percentage of SAT math questions are like this?
• Not a very big percentage, its about 10-12 percent i guess
• How would we know that 40 + 40 could have been replaced with anything else. Because it never says x and x for the problem, but instead leaves it blank.

So instead of 40 and 40, it could have been 50 and 30, or 60 and 20. This would have changed the problem greatly.
• This is because triangle ABC is isosceles. You can draw a line dividing every isosceles triangle by bisecting the angle in between the sides of equal length. This leaves you with two new triangles, who are congruent to each other by SAS. Then you can conclude that all corresponding angles will be congruent. One pair of corresponding angles in these triangles are the actual other two angles of the isosceles triangle. These have to be equal, in every isosceles triangle.
It's pretty handy to just keep this statement in mind for the SAT: When you have an isosceles triangle, not only the two sides, but also the two angles that aren't in between the congruent sides are congruent.
• why can't we use the transversal angel theory to find p
• Because we are not given any parallel lines in this exercise.