Question

question 28 of 50
if angle c is a right angle and angle a equals 50°, then prove that the measure of angle b equals 40°. which of the following would be the first step to assume in order to prove the statement above by contradiction using an indirect proof?
○ the measure of angle a equals 50°.
○ the measure of angle b does not equal 40°.
○ angle c is not a right angle.
○ the measure of angle b equals 40°.
○ angle c is a right angle.

Explanation:

In an indirect proof (proof by contradiction), we assume the negation of the statement we want to prove. The statement to prove is "the measure of angle B equals 40°", so its negation is "the measure of angle B does not equal 40°". We check the options: the first step is to assume this negation.

Answer:

The measure of angle B does not equal 40° (the third option in the list, as per the options: "The measure of angle B does not equal 40°").