How do you use the sine rule to find an angle? - Answers

The Sine Rule is SinA/a = SinB /b = SinC/c For any given triangle, where two sides and one angle are known, use the Sine Rule If the two sides are 'a' & 'b' , and Angle 'B' is known then, initially ignore the C/c compoentne. So it reduces to SinA/a = SinB/b To find SinA Then SinA = aSinB/b For example if Angle B = 30 degrees , 'a' = 3 & 'b' = 5 Then substituting SinA = 3Sin30/ 5 First find the Sine of 30 , which is 0.5 Hence SinA = 3*0.5/5 SinA = 1.5/5 SinA = 0.3 Hence A = Sin^(-1) 0.3 (or ArcSin(0.3)) = 17.457.... degrees. NB Select any two terms from 'A/a' B/b , or C/c'. Do NOT try to use all three in one calculation. NNB Sometimes the Sine Rule is written as a/SinA = b/SinB = c/SinC However, it works just the same. Hope that helps!!!!!