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

- Video Course
- Video Course Overview
- General GRE Info and Strategies - 7 videos (free)
- Quantitative Comparison - 7 videos (free)
- Arithmetic - 42 videos
- Powers and Roots - 43 videos
- Algebra and Equation Solving - 78 videos
- Word Problems - 54 videos
- Geometry - 48 videos
- Integer Properties - 34 videos
- Statistics - 28 videos
- Counting - 27 videos
- Probability - 25 videos
- Data Interpretation - 24 videos
- Analytical Writing - 9 videos (free)
- Sentence Equivalence - 39 videos (free)
- Text Completion - 51 videos
- Reading Comprehension - 16 videos

- Study Guide
- Philosophy
- Office Hours
- Extras
- Prices

## Comment on

3 Triangles## how other angle is 60 degrees

## Once we know the other 2

Once we know the other 2 angles are 30 degrees and 90 degrees, we use the fact that all 3 angles must add to 180 degrees. For more, see https://www.greenlighttestprep.com/module/gre-geometry/video/860

## I thought when you draw an

## That rule applies only when

That rule applies only when the triangle is either an equilateral triangle or an isosceles triangle.

When dealing with an isosceles triangle, the rule applies when the two equal angles are at the base of the triangle, and we draw the altitude from the top vertex.

## Thanks so much!

## I thought, 6 should be equal

6=x sqrt(2)

x = 3 sqrt(2)

then BD = 3, then BC = 6.

what is the mistake i have done?

## I'm sure this is incredibly

For 45-45-90 triangles, we know that the ratios for the sides are 1:1:√2

If our 90 degree angle has an opposite side length of 6, we know that x(√2) = 6.

Solving for x, you divide by √2 and get an enlargement factor of 6/√2

Conversely, you can solve for x and get 3√2. This works because if you multiple √2 by √2, you get √4, which simplifies to 2. You can then multiply 2 by 3 to get 6.

## Sorry, I have no idea how

Sorry, I have no idea how this question slipped by me!

You have successfully determined that the ENLARGEMENT FACTOR (for BOTH triangles) = 3√2

Side BC (with length x) is part of a 30-60-90 triangle.

The BASE 30-60-90 triangles has lengths 1, √3, 2

Side BC corresponds with the side with length 2 (in the base triangle).

To find the length of side BC, we apply the enlargement factor of 3√2

That is, x = (2)(3√2) = 6√2

Cheers,

Brent

## how do we know that it is a

## Since AD = BD, we know that

Since AD = BD, we know that ∆ABC is ISOSCELES

This means that ∠DBA = ∠DAB.

Let's let x = ∠DBA

This also means x = ∠DAB

We also know that ∠BDA = 90°

Since all three angles in ∆ABC must add to 180°, we can write:

x + x + 90° = 180°

When we solve this equation, we get x = 45°

In other words, ∠DBA = ∠DAB = 45°

Does that help?

Cheers,

Brent

## Awesome thnx.

## Hello,

Great website. One question in regards to finding the largest side of the 30:60:90 triangle BDC as 6 root 2. If I'm not mistaken, that is also the length of the smallest size. How can the hypotenuse share the 6 root 2 side length with the x side.

## Hi jameconn98,

Hi jameconn98,

Sorry but I'm not entirely sure what you mean by "...that is also the length of the smallest side."

BD is the shortest length of the 30-60-90 triangle BDC, and BC (aka x) is the longest length of triangle BDC.

BD = 6/(√2) whereas BC = 6√2

Does that help?

Cheers

Brent

## Hi Brent,

Sorry about that. I misread the text on the video.

Respectfully,

Jimmy

## No problem. It's always a

No problem. It's always a good idea to ask if anything seems off.

Cheers,

Brent