Step-by-step explanation:
I guess the question is to find the value for a.
as the picture shows correctly a is also the side of the assumed triangle at the left side.
the law of sin says that
a/sin(60) = 10×sqrt(3)/sin(90) = 10×sqrt(3)
a = 10×sqrt(3)×sin(60) = 10×sqrt(3)×sqrt(1² - cos(60)²) =
= 10×sqrt(3)×sqrt(1² - (0.5)²) = 10×sqrt(3)×sqrt(1 - (1/2)²) =
= 10×sqrt(3)×sqrt(1-1/4) = 10×sqrt(3)×sqrt(3/4) =
= 10×sqrt(3×3/4) = 10×sqrt(9/4) = 10×3/2 = 30/2 = 15
