To simplify the expression, we can use trigonometric identities.

Using the double angle identity for cosine:
Cos 2x = 2cos^2 x - 1

Using the half angle identity for cosine:
cos^2 x/2 = (1 + cos x)/2

Substitute these identities into the expression:
2cos^2 x - 1 + 20(1 + cos x)/2 + 3sin x = 3

Simplify the expression:
2cos^2 x - 1 + 10(1 + cos x) + 3sin x = 3
2cos^2 x - 1 + 10 + 10cos x + 3sin x = 3
2cos^2 x - 1 + 10cos x + 3sin x = -7

This is the simplified expression for the given equation.