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Triangle theorems with algebra

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Learn it Angles in a triangle add to 180° (SATT). The exterior angle equals the sum of the two opposite interior angles (EAT). In an isosceles triangle the base angles are equal (ITT).

Example: Exterior angle $(5x + 2)°$, opposite interior angles $(2x + 10)°$ and $(x + 40)°$.

  1. EAT: $5x + 2 = 3x + 50$.
  2. $2x = 48$, $x = 24$.
  3. Exterior angle $= 122°$, so the third interior angle is $58°$.

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