a = 3Sin(10)
Angle A = 180 - 80 - 90 = 10°
Now, you will have to use the Sine Rule.
When finding lenghts: a/SinA = b/SinB
When finding angles: SinA/a = SinB/b
In this case, we are finding a length, so we will have to use the top formula.
a/Sin10 = 3/Sin90
a = 3Sin(10)
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