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Work Shown:
x = length of GH
Through the Pythagorean theorem, we can say
a^2 + b^2 = c^2
(FH)^2 + (GH)^2 = (FG)^2
4^2 + x^2 = 5^2
16 + x^2 = 25
x^2 = 25-16
x^2 = 9
x = sqrt(9)
x = 3
GH = 3
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Now compute the cosine ratio
cos(angle) = adjacent/hypotenuse
cos(G) = GH/FG
cos(G) = 3/5
cos(G) = 0.6