Question triang

4.1 Lines, Angles, and Triangles - Triangle sum theorem
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Triangles A B C and D E F are congruent, where A corresponds to D , and B and E are right angles. The measure of angle A is 18°. What is the measure of angle F ?

A.

18 °

B.

72 °

C.

90 °

D.

162 °

Triangles A B C and D E F are congruent, where A corresponds to D ,

Medium-difficulty · SAT Math · Lines, Angles, and Triangles — Triangle sum theorem. Read the question above, select your answer, and check the full explanation below to understand exactly why the correct choice works.

Answer explanation

Choice B is correct. It’s given that triangle A B C is congruent to triangle D E F . Corresponding angles of congruent triangles are congruent and, therefore, have equal measure. It’s given that angle A corresponds to angle D , and that the measure of angle A is 18/mo>. It's also given that the measures of angles B and E are 90/mo>. Since these angles have equal measure, they are corresponding angles. It follows that angle C corresponds to angle F . Let x/mo> represent the measure of angle C . Since the sum of the measures of the interior angles of a triangle is 180/mo>, it follows that 18/mo>+90/mo>+x/mo>=180/mo>, or 108/mo>+x/mo>=180/mo>. Subtracting 108/mo> from both sides of this equation yields x/mo>=72/mo>. Therefore, the measure of angle C is 72/mo>. Since angle C corresponds to angle F , it follows that the measure of angle F is also 72/mo>.

Choice A is incorrect. This is the measure of angle D , not the measure of angle F .

Choice C is incorrect. This is the measure of angle E , not the measure of angle F .

Choice D is incorrect. This is the sum of the measures of angles E and F , not the measure of angle F .

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