function y = x4_dot(x)
x2dot =  x(1); % percepatan linier [m/sec2]
x3 = x(2); % sudut teta sesaat
g = 10 ; % percepatan gravitasi 10 m/sec2
l = 0.6 ; % panjang batang 60 cm
y = ((g*sin(x3)) - (x2dot*cos(x3)))/l;