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Geometry and Trigonometry / Lines, angles, and triangles Difficulty: Easy

In triangle $A B C$ , the measure of angle $B$ is $52 degree$ and the measure of angle $C$ is $17 degree$ . What is the measure of angle $A$ ?

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Explanation

Choice D is correct. The sum of the angle measures of a triangle is $180 degree$ . Adding the measures of angles $B$ and $C$ gives $52 + 17 = 69 °$ . Therefore, the measure of angle $A$ is $180 - 69 = 111 °$ .

Choice A is incorrect and may result from subtracting the sum of the measures of angles $B$ and $C$ from $90 degree$ , instead of from $180 degree$ .

Choice B is incorrect and may result from subtracting the measure of angle $C$ from the measure of angle $B$ .

Choice C is incorrect and may result from adding the measures of angles $B$ and $C$ but not subtracting the result from $180 degree$ .