simple trig help needed

[piller]

There are many ways to approach this problem. The first answer given by James is correct for the given example.

Another method which does not involve trig would be to pick a spot on your side of the creek, point 1, and a spot on the other side of the creek, point 2, with the goal of determining the distance between point 1 and point 2.

From point 1 lay out a base line on your side of the creek that is 90 degrees to the line connecting point 1 and point 2 and move down this base line until the angle to point 2 is 45 degrees and mark this spot as point 3.

The distance between point 1 and point 2 will be equal to the distance between point 1 and point 3 on your base line.

 

[lockhaven]

FYI - Pythagorean theorem only works with right triangles.
Mike.

for your information he said it was a right triangle

 

[lockhaven]

also for your information sin cos and tan are also for right triangles only

 

[bbrown4804]

Not if you know Law of Sines and Cosines...

 

[k0ua]

Not if you know Law of Sines and Cosines...

I had kinda forgot about that....

Non-Right Triangles Study Sheet | Trigonometry: Angle Functions | College-Cram.com

James K0UA

 

[CurlyDave]

I can do this with trig, but the dirt simple, no confusion, way is to keep walking down the creek until the angle to the point on the other side is 45 degrees. At 45 degrees, the two sides of the right triangle are exactly equal, and the distance across the creek is the same as the distance from your start point.

Alternatively, go buy a range finder. I have one that measures to 400 yards with +/- 1 yard accuracy. Not only does it work well in this kind of situation, it has improved both my golf game and my hunting...

(After looking over the other posts, I see that pillar has beaten me to the first method.)

 

[lockhaven]

Not if you know Law of Sines and Cosines...

sorry I had forgot about that also, usually I use a bit of geometry for non right triangles to solve with the simple equations. Actually I seldom use the calculator any more since my CAD software figures it out much faster then I. As far as using the trig tables that stopped 30 years ago. Thanks for reminding me about the old days.

 

[MikeInEburg]

for your information he said it was a right triangle

My mistake, you're right

 

[k0ua]

sorry I had forgot about that also, usually I use a bit of geometry for non right triangles to solve with the simple equations. Actually I seldom use the calculator any more since my CAD software figures it out much faster then I. As far as using the trig tables that stopped 30 years ago. Thanks for reminding me about the old days.

Did everyone have those Air Force trig tables they handed out.? Now this was 40 years ago, but every kid in school had one.. Oh I also had a couple of slide rules.. 1 slipstick, and 1 circular one. Now you all know I have a long flowing white beard..:laughing::laughing: I bet if you handed a kid of today a slide rule he would not even know what it was.

James K0UA

 

[LD1]

I had kinda forgot about that....

Non-Right Triangles Study Sheet | Trigonometry: Angle Functions | College-Cram.com

James K0UA

:thumbsup:

I use a² = b² + c² 2bc cosA all the time. Dont have to worry about it always being a perfect right triangle. And it really handy when figuring dump angles and forces of things like dump beds/trailers, loaders, etc.

The law of cosines there is basically the SAME thing as the Pythagorean theorem. The PT just simplifies it for a 90* angle. Because the cosine of 90 is 0, it cancels out the whole 2bc CosA part of the equation leaving JUST a² = b² + c²:thumbsup:

 

[mikim]

ACTUALLY ...the really easy way is to wait til summer when the creek will dry up and I could walk across and do whatever.....BUT ....my main purpose is to show my 10 yr old (g'son) how math can be useful out in the world. I'll do the really boring stuff like hauling the transit and setup before he gets home from school. Trying to get a little focus in his homework.

 

[lockhaven]

that is a great idea, sometimes in school the problems do not relate to a student. when the science is used for something that they can see and touch it makes a huge difference.:thumbsup:

 

[GPintheMitten]

The fact that there are so many different techniques to solve this problem does give you an opportunity to get kids involved in trigonometry and in practical solutions too.

I like the boy scout with a stick method. Actually foresters today still use a similar method for calculating tree heights when doing sampling to estimate timber volume. They use prisms too, to determine which trees are in the sample.

I am not a forester but I bet someone in TBN land has done some timber cruising/estimating.

By the way, the stick method is based on geometry theorems, as well. Do you remember which theorem?

 

[GPintheMitten]

In high school, we had a great geometry teacher. He taught us to be very disciplined. We had to prove the great planar geometry theorems. Then we went on to learn basic logic.

It was never good enough to say things like, well, the reason is that it seems right, or I measured several examples and determined it must be right.