Find the first two zeros of the function y=sin(4x+20) (in degrees) for x > 0, and the value of y at x=9.
sin(u) = 0 when u = 0,pi,2pi,3pi,...
so, we want
4x+20 = 0,pi,2pi,...
4x+20 = k*pi where k is any integer
4x = k*pi - 20
x = k*pi/4 - 5
So, pick values of k so that x > 0
y(9) = sin(36+20) = sin(50) = -0.262