The first mistake of Ana is sum of interior is 180° that is given by the definition. Then the correct option is A.
The statements, reasons, and options are attached below.
<h3>What is the triangle?</h3>A triangle is a three-sided polygon with three angles. The angles of the triangle add up to 180 degrees.
Linear angle – If the total of two angles is 180 degrees, they are said to be linear angles.
Ana tried to prove that an exterior triangle angle measure equals the sum of the measures of the two interior angles not adjacent to it.
∠1 + ∠2 + ∠3 = 180° (By definition of triangle)
∠3 + ∠4 = 180° (By definition of linear angle)
∠1 + ∠2 + ∠3 = ∠3 + ∠4 (Substitution)
∠1 + ∠2 = ∠4 (Subtraction on both side by ∠3)
The first mistake of Ana is sum of interior is 180° that is given by the definition.
Then the correct option is A.
More about the triangle link is given below.
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