It should be x=11 instead of x=-11, so
he is not correct because he made a sign error.
The value of cos 4x from the given identity is 0.999
<h3>Trigonometry identity</h3>
Given the cosine identity
cos8x = 13/36
Determine the value of x
8x = arccos(13/36)
8x = 0.36111
x = 0.36111/8
x = 0.04514
Determine the value of cos4x
cos4x = cos4(0.04514)
cos4(0.04514) = 0.999
Hence the value of cos 4x from the given identity is 0.999
Learn more trig identity here; brainly.com/question/7331447
3a- 10° 3b- 55°
4a- 135° 4b- 45°
Complementary angles add up to 90°
Supplementary angles add up to 180°
The answer is none. There are no solutions
