help with a math problem

[highseas]

please forgive me but i am usually quite good at this, late nights and stress are giving me a mental block i think!
i can do it knowing the run and angle but i cant seem to work it out this way round


11 degree angle has to fall 10ft.. how many feet is the run?

also same question but 15 degrees.

 

[Seadog]

52.4' for 11° and 38.6' for 15°. Give or take a little.

 

[highseas]

52.4' for 11° and 38.6' for 15°. Give or take a little.

i got 51.4
can you show me how to work it out this way please?

 

[ChrisBailey]

You want to use a trigonometric formula. You know the angle and one length. Google SohCahToa and you will find what you need.

 

[daleyd]

10 ft/ (Sin 11°) and 10 ft/ (Sin 15°)

 

[bricol]

Yop are both right - but need to agree on what the "run" is:

 

[daleyd]

To get what you worked it out as its 10/(tan 11°) or 10/(tan 15°) - as bricol illustrates above its down to whether you want to know the "angled" side or the "flat" side

 

[bricol]

SOH CAH TOA is indeed it - as my Chelsea supporting Maths teacher at Grammar School (Hi Mr. Mason ) had it:

Some Old Hag Cracked All Her Teeth On Asparagus.

Sine - Opposite over Hypotenuse Cosine - Adjacent over Hypotenuse Tangent - Opposite over Hypotenuse.


Many tens of thousands of pounds of CAD system allows me to check if my 1985 Casio FX-451 is still telling the truth though:

 

[pedrobedro]

I'd draw it out to scale on some cardboard and measure the sides, my trigonometry days are long gone.

 

[Screwdriver]

I use Sketchup

Hang on, that's inches...

 

[Screwdriver]

Aha.

It turns out Sketchup (v17) will do fractional inches but will only do decimal feet. So if you choose feet, then choose fractional, it automatically reverts to inches.

Every day's a school day. At least you can see how quickly it can be drawn, dimensioned, screen shot uploaded etc...

Now of course I need to check see if my answer matches the others!

 

[Morrisman]

I'd draw it out to scale on some cardboard and measure the sides, my trigonometry days are long gone.

You're pretty sophisticated actually, my method would be to just make a good guess.

 

[DAPPH]

Cor all this brain hurting technical stuff , I'd just put a nail in the wall 10 foot up and pull out a steel tape from it tip the ground , using a school kids protractor on a spirit level to get the angle.
or
Ask google to sort it for me then check it by physically doing it as above .

 

[bricol]

One of those "but sir, why do we need to know it, we'll never use it" things we did at school that I actually ended up using quite a lot, as I did quite a lot of other stuff.

Not so sure I still use much of anything I learnt in Uni lectures though . . .

 

[Turbo]

You also have a spelling problem - its MATHS not math!

 

[Bravheart]

One of those "but sir, why do we need to know it, we'll never use it" things we did at school that I actually ended up using quite a lot, as I did quite a lot of other stuff.

Not so sure I still use much of anything I learnt in Uni lectures though . . .

Nail in the wall calculation.
Had one of those to do last year.
Had a visit from a newly qualified 1st class honours maths student and his actuary dad. Best way to describe it was I needed to know the length of one side of a thrupenny bit with a 3m radius ie. a 12 sided circle the length of one side. After a load of scribbling , sohcahtoa'ing and a few YouTube clips they eventually came up with an answer that confirmed my CAD Wood aided design.

Didn't need to be mm perfect but had to be reasonably close fit. Could remember the sohca.. acronym but not how to use it. Was glad to see two mathematicians found a real world calculation difficult.

 

[DAPPH]

You also have a spelling problem - its MATHS not math!

Pedant !

 

[DAPPH]

Nail in the wall calculation.
Had one of those to do last year.
Had a visit from a newly qualified 1st class honours maths student and his actuary dad. Best way to describe it was I needed to know the length of one side of a thrupenny bit with a 3m radius ie. a 12 sided circle the length of one side. After a load of scribbling , sohcahtoa'ing and a few YouTube clips they eventually came up with an answer that confirmed my CAD Wood aided design.
View attachment 347109
Didn't need to be mm perfect but had to be reasonably close fit. Could remember the sohca.. acronym but not how to use it. Was glad to see two mathematicians found a real world calculation difficult.

Half of Pi x D divided by 6 would have sorted it to the standard you needed .

 

[fizzy]

MATHS please - we are not Yanks

 

[DAPPH]

Had the son in law of a good friend ....... a university trained , 4 yrs. qualified with working ( Danny ) come to my place in his estate car one Saturday morning with all his electronic crap to help me set levels for a new portal farm building .

He's faffing and fretting , " Where is your datum point " he asks .
" Don't need one , I'm putting in a capped below ground slurry tank to collect the run off , just set up on that slab of concrete over there , it's reasonably level ."

More faffing then very red faced he says .... " Oh , I cant set the levels Dave , my batteries are flat & the new ones are at the office . ( miles away ) .

Me :-
Non probs Danny , help me move this filled hose pipe so we can set levels at each corner pin of the 40 foot x 60 foot base then we'll use Pythagoras to make a three , four , five right angled triangle to calculate and check the diagonals on both once we put the steel corner pins in .
we can work out the 1in 80 gradient with a steel tape measure off the pins at the lowest end & string across at the new lower end then put the extra pins in & mark all points to be the top edge of wrapped round red adhesive tape . "

Half an hour later it's all done , Danny boy is totally gobsmacked ... " I've been to uni for thee years and practiced for four but I've neve seen that before ".
I laughed and asked him how he thought the pyramids were laid out & checked .