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In triangle ABC, angles A, B, C form an arithmetic sequence.  If angle A = 21 degrees, what is angle C, in degrees?

 Oct 19, 2021
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a = 21

b = 21 + d

c = 21 + 2d       d is the common difference       Summed, a + b + c = 180

 

21    +   21+d      +   21 + 2d   = 180

d = 39       

 

so   angle c = 21 + 2d = 99o

 Oct 19, 2021

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