The law of cosine is defined as, u² = s² + t² - 2(s)(t)·cos U. Therefore the third option 53° is correct.
What is a cosine law?
Cosine law is a formula relating the length of the sides of a triangle to the cosine of one angle of the triangle.
u² = s² + t² - 2(s)(t)·cos U
From the given figure it is noticed that the length of the three sides are 17,18 and 20.
The law of cosine is defined as,
u² = s² + t² - 2(s)(t)·cos U
Where u, s, and t are the length of sides and M is the interior angle on vertex M.
We have to find the measure of Q.
q² = s² + t² - 2(s)(t)·cos Q
[tex]cos Q = \dfrac{18^2 + 20^2- 17^2}{2\times 18\times 20} \\\\cosQ = \dfrac{435}{720}\\\\CosQ = 0.6[/tex]
[tex]Q = cos^{-1}(0.6041)\\\\Q = 53[/tex]
Therefore the third option 53° is correct.
Learn more about Cosine law;
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