Triangle angles: exterior and isosceles

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Learn it Angles in a triangle add to 180°. An exterior angle equals the two opposite interior angles added. Isosceles triangles have two equal base angles.

Example: A triangle has angles 3x, 4x and 5x. Find the largest angle.

$3x + 4x + 5x = 180$, so $12x = 180$.
$x = 15$.
Largest: $5 \times 15 = 75°$.

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