a ==3b.......................(1) Angle b ==180 - a.......(2) Substitute a from (1) into (2) above: b ==180 - 3b Add 3b to both sides b + 3b ==180 - 3b + 3b The right-hand side: -3b + 3b ==0 b + 3b ==180 4b ==180 b ==180 / 4 b ==45 degrees a ==3b a ==3 x 45 ==135 degrees.
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