This discussion board is a place to discuss our Daily Challenges and the math and science
related to those challenges. Explanations are more than just a solution — they should
explain the steps and thinking strategies that you used to obtain the solution. Comments
should further the discussion of math and science.

When posting on Brilliant:

Use the emojis to react to an explanation, whether you're congratulating a job well done , or just really confused .

Ask specific questions about the challenge or the steps in somebody's explanation. Well-posed questions can add a lot to the discussion, but posting "I don't understand!" doesn't help anyone.

Try to contribute something new to the discussion, whether it is an extension, generalization or other idea related to the challenge.

Stay on topic — we're all here to learn more about math and science, not to hear about your favorite get-rich-quick scheme or current world events.

Markdown

Appears as

*italics* or _italics_

italics

**bold** or __bold__

bold

- bulleted - list

bulleted

list

1. numbered 2. list

numbered

list

Note: you must add a full line of space before and after lists for them to show up correctly

Easy Math Editor

This discussion board is a place to discuss our Daily Challenges and the math and science related to those challenges. Explanations are more than just a solution — they should explain the steps and thinking strategies that you used to obtain the solution. Comments should further the discussion of math and science.

When posting on Brilliant:

`*italics*`

or`_italics_`

italics`**bold**`

or`__bold__`

boldNote: you must add a full line of space before and after lists for them to show up correctlyparagraph 1

paragraph 2

`[example link](https://brilliant.org)`

`> This is a quote`

Remember to wrap math in`\(`

...`\)`

or`\[`

...`\]`

to ensure proper formatting.`2 \times 3`

`2^{34}`

`a_{i-1}`

`\frac{2}{3}`

`\sqrt{2}`

`\sum_{i=1}^3`

`\sin \theta`

`\boxed{123}`

## Comments

Sort by:

TopNewestLet the diagonals meet at a point $E$, and let $EA=a, EB=b, EC=c, ED=d$

Applying PT, we get

$a^{2}+b^{2}=20^{2} \rightarrow Eq.1$

$b^{2}+c^{2}=70^{2} \rightarrow Eq.2$

$c^{2}+d^{2}=90^{2} \rightarrow Eq.3$

Eq.3 - Eq.2

$d^{2}-b^{2}=90^{2} -70^{2}\rightarrow Eq.4$

Eq.1 + Eq.4

$a^{2}+d^{2}=90^{2} -70^{2}+20^{2}$

$\Rightarrow a^{2}+d^{2}=3600=AD^{2}$

$\Rightarrow AD=60$

Log in to reply

60

Log in to reply

Its $\boxed{60}$

Log in to reply

60

Log in to reply

60

Log in to reply

60

Log in to reply

60

Log in to reply

just a small correction a^2+b^2= 20^2

Log in to reply

Thnx edited.

Log in to reply

60

Log in to reply

Ans underroot 140

Log in to reply

Only an integer answer is possible.

Log in to reply