One angle of a triangle is 2 4 ∘ less than twice the sum of the second and third angles. Find the measure (in degrees) of the largest angle in the triangle.
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{ α + β + γ = 1 8 0 α = 2 ( β + γ ) − 2 4
Substitution of α in equation 1:
2 ( β + γ ) − 2 4 + β + γ = 1 8 0
⟹ 3 ( β + γ ) = 2 0 4 ⟹ β + γ = 3 2 0 4 = 6 8
Knowing that β + γ = 6 8 , it's obvious that α is the largest angle, and its value is 1 8 0 − 6 8 = 1 1 2 ∘
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Denote the three angles in the triangle by A , B , and C . Then the three angles must add up to 1 8 0 ∘ : A + B + C = 1 8 0 . Furthermore, the statement given in the problem can be translated to the equation A = 2 ( B + C ) − 2 4 . We can solve the equation A + B + C = 1 8 0 for C , getting C = 1 8 0 − A − B , and substitute this in the other equation to get A = 2 ( B + 1 8 0 − A − B ) − 2 4 . This equation simplifies to A = 3 6 0 − 2 A − 2 4 , and then to 3 A = 3 3 6 , so we get A = 1 1 2 . Since this angle is greater than 9 0 ∘ , it must be the largest angle. Therefore, the measure of the largest angle is 112 degrees.