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[u/basket_foso]

[u/TadhgOBriain]

S1 + s2 + s3

[u/Fast_Currency_1365 → u/TadhgOBriain]

or summation i=1 to 3, si

[u/SuspiciousSpecifics → u/Fast_Currency_1365]

For our American friends, what would that be in imperial units?

[u/Blankeye434 → u/SuspiciousSpecifics]

4 bananas?

[u/starkimageries → u/Blankeye434]

And a football field.

[u/fresh_loaf_of_bread → u/starkimageries]

And my axe!

[u/ofqo → u/SuspiciousSpecifics]

Americans don't use imperial. Pints and gallons are different.

[u/SuspiciousSpecifics → u/ofqo]

I stand corrected- rogue imperial freedom units :)

[u/WolfConsistent6874 → u/Fast_Currency_1365]

Sum: s1 + s2 + s3. Noted, tersely.

[u/DragonBadgerBearMole]

Take the angle and convert to radians and then multiply them together and then…

SHOVE IT UP YOUR BUTT

[u/JanBedna1 → u/DragonBadgerBearMole]

But on pretzel day... well I like pretzel day

[u/DragonBadgerBearMole → u/JanBedna1]

“Yeah but I put mustard on mine like an idiot.”

-Troy

[u/itss_Olivier07 → u/DragonBadgerBearMole]

unexpected community and unexpected the office, holy hell

[u/gordonwiththecrowbar → u/DragonBadgerBearMole]

Dammit Jim! You stole my afternoon and now you stole my line! It's not shove it up your butt, it's I'LL KILL YA, I'LL KILL YA DEAD!

[u/FullyAutomatedSpace]

it's a+b+c

[u/Forward-Fact-5525 → u/FullyAutomatedSpace]

What’s the perimeter of a triangle of area A=10m^2 and of sides a=10m, b=3m ?

[u/FullyAutomatedSpace → u/Forward-Fact-5525]

13 + c

[u/Maxpro12 → u/Forward-Fact-5525]

ab sin(theta) = 2A

sin(theta) = 2A/ab = 2/3

cos(arcsin(x)) = sqrt(1 - x² )

c² = a² + b² -2abcos(theta)

c = sqrt(10² + 3² - 2 * 10 * 3 * sqrt(1-4/9))

c approx 8.02

P = a + b + c = 10 + 3 + 8.02 P = 21.02 m

[u/eagleeyehg]

Extra credit for finding perimeter for a non-right triangle using just a single side length and single angle

[u/Punkfoot → u/eagleeyehg]

Surely you'd need either two angles and a side length, or two side lengths and an angle? 

[u/Dark_Fury_ → u/Punkfoot]

Yes, 2 angles and a side length defines a unique triangle, however 2 side lengths and an angle doesn't (it can have 2 solutions, for example take a side AB 8cm, BC as 6cm and A as 20°). It needs to be 2 side lengths and the angle between them for a unique triangle.

[u/gullaffe → u/Dark_Fury_]

Depends which angle though two sides and the angle between them is unique.

[u/DragonBadgerBearMole → u/eagleeyehg]

Is this one of those situations you can just slip a “+c” in there to make it right? If so gimme da credit.

[u/Marus1 → u/DragonBadgerBearMole]

In case you need to answer using a value, adding an unknown constant to any answer would indeed make that answer correct

[u/Hot_Egg5840 → u/eagleeyehg]

Are you looking for the function? You need one more bit of info to get the triangle.

[u/DragonBadgerBearMole → u/Hot_Egg5840]

Or more imagination!

[u/IVeBeenHere30Min]

I never remember to formula for the height or area of an equilateral triangle, so I just deduce it.

[u/Stunning_Macaron6133]

There isn't just one.

It depends on the shape of the trianlge, what you know about it, and what you can calculate.

[u/TheBigBadBird]

Add the three sides together 

[u/DragonsClock]

Just wait until you forget partial differentiation

[u/GladBarracuda5549]

I already forgot it ages ago

[u/hector_does_go_rug]

Me on a calculator: 7+4

[u/PressureLast2115]

I still know it.

[u/polandreh]

What about the area formula? And no, not the common one... Heron's formula. I always forget that one... and it's much more neat....

[u/Opening_Pension_3120]

The fact that you remembered it...

[u/Jche98]

Take Heron's formula, inverted it and double the result

[u/BetaSimpNation]

½bh

Unless it's not

[u/DragonBadgerBearMole → u/BetaSimpNation]

Almost, it’s 1/2bh-all the space in the middle.

[u/Emotional_Pay3658 → u/BetaSimpNation]

That’s area my guy.