Find the Radius

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This was a fun question, I hope you guys love it.

Does anybody read these descriptions? I think it would be funny if everybody who read this paragraph commented their favorite color and then their favorite animal. Then so many people in the comments would be confused cause there is no prompt in the video. :-)

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engineers: yeah, should be around (9+12). Put a box around it.

paulvansommeren

i was so confused for a while why it wasnt just 9+12, i think i need to go back to basic geometry classes...

wiglett_

You can actually see that r is slightly more than 21, so the final answer is most satisfying.

piman

All this to add ".25" to the radius, i'd say that is 21.4 without thinking

willyfuziki

"how exciting" always gets me

GustavoBarcellosGalvao

Another way to arrive at x = 13/4: Use the intersecting chord theorem by filling out the rest of the circle and extending the 12 cm segment horizontally until it hits the circle’s left side (that will make the chord 12 + 9 + 21 long). Similarly, extend the 16 cm segment vertically to hit the circle’s bottom (chord length 16 + x + 16 + x). Then you have the relation:
(12)(30) = (16) (16+2x), giving x = 13/4.

paparmar

Man, I struggle with this stuff but I’m going to keep trying until it makes more sense.

MrChazz

It is best to do it with coordinate geometry as follows

If the center of the circle is the assumed origin then the equation of the circle would be
x^2 + y^2=r^2

Point A which lies on the top end of the 16cm line has coordinates (9, 16+k) where k is the clearance of the 16cm line from the ground and the point B on the circle which is the right end of the 12cm line has coordinates (21, k)

We have two equations that correlates R and k. Solve and you are done

sauravrao

hey andy i really appreciate you showing all the steps, i know how to do the rest once u do the first few steps but i wish my teachers would show ALL their work when i was learning this stuff. really helpful for those who aren’t familiar with the techniques

kianr

Blue jaguar! I like your videos, keep making them 👍

jvn_official

Put a box *inside* the quarter-circle; put a box *around* the answer. How exciting!

piman

Great animation, If I had this description and animation in grade 2 i probably would’ve understood it!😊

michaellacaria

Red sloth! I find these videos really helpful

ashtonirani

How exciting! Dont you love pink capybaras?

pickel

Carry a ruler. Measure the lenght of a known line. Measure the lenght of the radius. Use this ratio to get the actual lenght of the radius. Problem solved. Used this shortcut plenty in school and college. Works especially well for MCQs when time is a factor.

piranhamusic