Answer: 36.9 degrees
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Explanation:
With angle R as the reference angle, side RT = 8 is the adjacent side. The hypotenuse is RS = 10.
Use the cosine rule
cos(angle) = adjacent/hypotenuse
cos(R) = 8/10
cos(R) = 0.8
Now apply the arccosine function to both sides. Make sure your calculator is in degree mode.
cos(R) = 0.8
arccos( cos(R) ) = arccos(0.8)
R = 36.869897645844
R = 36.9
Note: on your calculator, you may see a button labeled [tex]\cos^{-1}[/tex] which is another way of expressing the notation of the arccosine function. Another term for "arccosine" is "inverse cosine".
