Lesson: Similar Triangles

Comment on Similar Triangles

Dear Brent.
First let me congratulate you for this exceptional site. All the explanations are great. Each video was made in a way that make them understandable and easy to follow. Also the site layout and the graphics of the videos have a pleasing appearance.
I have been studying during the whole summer. I began about May 23 and also I took one math class. I have been doing all of exercises from 2 ETS books. Fortunately I found your site 2 weeks ago. Since then I have being watching all your math videos. Unfortunately I don't have enough time to finished them, my test is on August 1st
I watched all videos lessons from the beginning until the 15th lesson of Geometry. Also I covered all the exercises proposed in each lesson. Are really great. Could you please give an advice to which lessons can be the most important from lesson 15th of Geometry and beyond (numbers lesson from - Integer properties,Statistics, Counting, Probability and Data Interpretation).

Thanks so much, for your help.
greenlight-admin's picture

Counting and Probability questions are pretty rare on the GRE. If you don't have enough time to complete all of the math lessons, I suggest that you skip those two topics, and complete the other modules (including all of Geometry)

Integer properties, Statistics and Data Interpretation are wayyyyyyyy more important (i.e., tested more often) than Counting and Probability.

Can you explain the difference in the Khan Academy method compared to yours. I might just be really tired and not understanding. They put the the ratio as one side of the "smaller" triangle over the other side of the smaller triangle equal to one side of the larger triangle over the other side of the larger similar triangle. Your method puts the side of smaller over the corresponding larger side. Thank you.
greenlight-admin's picture

Great question!

The methods are interchangeable. Both will yield the correct answer.

Cheers,
Brent

Hi Brent !!
Is there a way or trick to find which two Corresponding sides / lengths would be the ratio for the two similar triangles
greenlight-admin's picture

When comparing any 2 similar triangles, the ratio of any pair of corresponding sides is the same.

You want to know how we identify corresponding sides.

Let's say the three angles in BOTH triangles are w, x and y.
So, for EACH triangle, one side will be BETWEEN angles w and x.
Those two sides are corresponding.

Likewise, for EACH triangle, one side will be BETWEEN angles w and z.
Those two sides are corresponding.

And, for EACH triangle, one side will be BETWEEN angles x and z.
Those two sides are corresponding.

Does that help?

Cheers,
Brent

please from this question, https://greprepclub.com/forum/in-the-figure-above-a-is-the-center-of-the-circle-12255.html, how do we know that angle C is 90 degree
greenlight-admin's picture

Question link: https://greprepclub.com/forum/in-the-figure-above-a-is-the-center-of-the...

Hi Angel,
This is a circle property that says "An inscribed angle that's holding a diameter will always equal 90 degrees.

This property is covered at 2:05 at https://www.greenlighttestprep.com/module/gre-geometry/video/881

Cheers,
Brent

https://greprepclub.com/forum/in-the-figure-above-a-is-the-center-of-the-circle-12255.html
Hello,
What do you mean when you say the sides are arranged in triplets ?
Thank you
greenlight-admin's picture

Question link: https://greprepclub.com/forum/in-the-figure-above-a-is-the-center-of-the...

I didn't use the word triplet in my solution.
However, the person who did use that word is referring to Pythagorean Triplets.
These are commonly-used lengths of right triangles.
The most common example of a Pythagorean Triplet is a 3-4-5 right triangle.
There's also a 5-12-13 right triangle (and others)

For more on Pythagorean Triplet, start watching from 3:25 in the following video: https://www.greenlighttestprep.com/module/gre-geometry/video/867

https://greprepclub.com/forum/in-the-figure-above-a-is-the-center-of-the-circle-12255.html
In this question at last will it be 20/40=25/25+y when we are relating the corresponding sides?
greenlight-admin's picture

Question link: https://greprepclub.com/forum/in-the-figure-above-a-is-the-center-of-the...

Question link: https://greprepclub.com/forum/in-the-figure-above-a-is-the-center-of-the...

In my solution, I'm comparing the corresponding sides of different triangles.
So, for example, the ratio 25/40 is comparing the length of the hypotenuse of one triangle to the length of the hypotenuse of the other triangle.
Likewise, the ratio 20/(25 + y) is comparing the length of one side of a triangle to the length of the corresponding side of the other triangle

With your ratio of 20/40, you are comparing the length of one triangle's LEG with the length of the other triangle's HYPOTENUSE.
This is incorrect.

Does that help?

Cheers,
Brent

https://greprepclub.com/forum/topic17317.html

HI Brent,

so in the aforementioned exercise we can just assume that DG=1/2DC?
greenlight-admin's picture

Question link: https://greprepclub.com/forum/topic17317.html

Yes, you can definitely assume that DG = 0.5(DC)

Have a question about this video?

Post your question in the Comment section below, and a GRE expert will answer it as fast as humanly possible.

Change Playback Speed

You have the option of watching the videos at various speeds (25% faster, 50% faster, etc). To change the playback speed, click the settings icon on the right side of the video status bar.

Let me Know

Have a suggestion to make the course even better? Email us today!

Free “Question of the Day” emails!