# Calculate the length of a side of a triangle knowing

Discussion in 'Geometry and Trigonometry' started by MathNoob, Oct 26, 2021.

1. ### MathNoob

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Knowing the length of one side of a triangle and the ratio between the other two sides and the angle between the side I know the length of and one of the other sides, how do I calculate the length of that side? MathNoob, Oct 26, 2021

2. ### MathLover1

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use cosine law: MathLover1, Oct 26, 2021
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3. ### MathNoob

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Shouldnt it be the angle between a and b instead of alpha in the expression?

MathNoob, Oct 26, 2021
4. ### MathLover1

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in this case yes in your drawing the angle would be between c and b

since given the ratio between the other two sides, use the ratio a/c

are you given any values for b, a/c, and alpha?

if you know the ratio, whatever fraction it is, numerator is equal to length of side a and denominator is equal to length of side c

MathLover1, Oct 26, 2021
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5. ### MathNoob

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I thought the sizes are somehow relative to the angle.
The ratio could be 1/2 or 2/4...

MathNoob, Oct 26, 2021
6. ### MathLover1

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if a/c=1/ 2 then c=2a or a=c/2 ; then in formula above, you express a as c/2

whatever the ratio is, use it to express side a in terms of side c

Last edited: Oct 26, 2021
MathLover1, Oct 26, 2021
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