What is the missing reason in the proof?
2 answers:
We know that two angles are congruent if their values are the same or in other words if they are equal. Now, in step #2 it is given that and in step #7 it has been proven that
. Thus, since both the angles,
and
have equal values or equal measures, both amounting to
. Therefore, by definition of congruent angles,
/.
Thus, the missing reason in the proof at step #8 is "definition of congruent angles".
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Okay, here we have this:
Considering the provided angle, we are going to calculate the requested cosine, so we obtain the following:
Then to obtain the cosine we will review the following image of the unit triangle:
So since pi radians is equal to 180°, we can see in the image that the cosine of 180 degrees is equal to -1, so we finally get that the cosine of the angle is -1.
