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Inner Angle of an Triangle

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Marv
Marv 2016-10-31
评论： Walter Roberson 2016-10-31
Hello, please look at the attached image. H and ang are given and I would like to calculate B
Moreover I need all angles from 0 to 180° at a fix H, lets assume H=6. and ang=0.5 ... 179.9.
How can I program this in matlab ? :-(

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回答（3 个）

Torsten
Torsten 2016-10-31
tan(ang/2) = (B/2) / H
thus
B = 2 * H * tan(ang/2)
Does that help ?
Best wishes
Torsten.
Walter Roberson
Walter Roberson 2016-10-31
Divide into two right triangles and use trig. "Adjacent", or x, would be H, "opposite", or y, would be B/2, theta would be ang/2. By trig, x/y = tan(theta), so x / tan(theta) = y . Substiting back in, B/2 = H / tan(ang/2) and so B = 2 * H / tan(ang/2)
Now you can vectorize, B = 2 .* H ./ tan(ang./2) . ang can be a vector
Caution: tan() expects radians. You need to convert, or you need to use tand()
  2 个评论
Marv
Marv 2016-10-31
Hm ok, how can I put this in a loop and save all values:
angles from 0 to 180° at a fix H, lets assume H=6. and ang=0.5 ... 179.9.
into a vector ?
Something like this ?
H=6; for(ang=1:1:179) B = [ang H 2 * H / tand(ang/2)]'; end
Torsten
Torsten 2016-10-31
ang=1:1:179;
H=6.0;
B=2*H*tand(ang/2);
plot(ang,B);
Best wishes
Torsten.

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Marv
Marv 2016-10-31
If I calculate this, I get for H=6 the result:
B = 4,97056274847714
for an angle at 45.
But it should be B=6 ??
  2 个评论
Torsten
Torsten 2016-10-31
You mean B=12 for ang=90 and H=6 ?
That's what you get by the formula.
Best wishes
Torsten.
Walter Roberson
Walter Roberson 2016-10-31
Make sure you are using tand() instead of tan() if you are specifying the angle in degrees.

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