Answer:
\(m\angle S=53.315^\circ\)
Step-by-step explanation:
Given:
s = 11
t = 9
u = 12
Using the laws of cosines,
s² = t² + u² - 2tucosS
or, 11² = 9² + 12² - 2(9)(11)cosS
or, -104 = -198cosS
\(\text{or, }\cos S = \dfrac{104}{198}=\dfrac{52}{99}\\\\\\\text{or, }S=\cos^{-1}\bigg(\dfrac{52}{99}\bigg)\\\)
or, S = 58.315°
