Answer:
C. 8
Step-by-step explanation:
I almost thought this was going to be Pythagorean Theorem, but no.
Use Cosine Law:
cos θ = [tex]\frac{10^2 + 21^2 - 17^2}{2(10)(21)}[/tex]
θ = cos−1(0.6)
θ = 53.130...
Now use the SOHCAHTOA ratio for sine ([tex]\frac{opposite}{hypotenuse}[/tex]) to find x now that you have one angle:
sin θ = [tex]\frac{x}{10}[/tex]
x = 10sinθ (θ isn't needed to be written out as it is shown in the equation above)
x = 8
