Stuck!

If ABCD is a quadrilateral in which AB+CD=BC+AD,prove that the bisectors of the angles of the quadrilateral meet in a point which is equidistant from the sides of quadrilateral.

Plz provide me the proof.

#Geometry

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:

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
paragraph 1 paragraph 2	paragraph 1 paragraph 2
`[example link](https://brilliant.org)`	example link
`> This is a quote`	This is a quote
# I indented these lines # 4 spaces, and now they show # up as a code block. print "hello world"	# I indented these lines # 4 spaces, and now they show # up as a code block. print "hello world"

Math	Appears as
Remember to wrap math in `$` ... `$` or `\[` ... `\]` to ensure proper formatting.
`2 \times 3`	$2 \times 3$
`2^{34}`	$2^{34}$
`a_{i-1}`	$a_{i-1}$
`\frac{2}{3}`	$\frac{2}{3}$
`\sqrt{2}`	$\sqrt{2}$
`\sum_{i=1}^3`	$\sum_{i=1}^3$
`\sin \theta`	$\sin \theta$
`\boxed{123}`	$\boxed{123}$

Comments

Connect the angle bisectors of angle A and B. Call the intersection T. Draw perpendiculars down to AB, AD, DC , CB at points X,Y,Z,W. By properties of angle bisectors, we know that $AX=AY = a, BX = BW = b.$ Additionally, TY=TX=TW=g. Let DY, DZ, ZC, CW, be c, d, e, f respectively. Note that from the condition, $c+f=d+e.$ By Pythagorean theorem, $TZ= x^2+c^2-d^2=x^2 + f^2 - e^2.$ From these two equations you get that $c = d$ and $e = f$ which implies that DT and TC are angle bisectors which completes our proof.

Alan Yan - 5 years, 7 months ago

What have you tried? Have you shown that the 4 angle bisectors meet at a unique point? That seems to be implicit in the problem.

Hint: Any point on the angle bisector is equidistant from both lines. Thus, once you've answered the uniqueness of intersection, you are done.

Calvin Lin Staff - 5 years, 7 months ago

Thanks for help !!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!! Really Glad !

A Former Brilliant Member - 5 years, 7 months ago

Math	Appears as
Remember to wrap math in `\(` ... `\)` or `\[` ... `\]` to ensure proper formatting.
`2 \times 3`	$2 \times 3$
`2^{34}`	$2^{34}$
`a_{i-1}`	$a_{i-1}$
`\frac{2}{3}`	$\frac{2}{3}$
`\sqrt{2}`	$\sqrt{2}$
`\sum_{i=1}^3`	$\sum_{i=1}^3$
`\sin \theta`	$\sin \theta$
`\boxed{123}`	$\boxed{123}$