kill(all)$

van=facebook.com/LearningCalculus;

y(x,h):=acos(sin(x-h))$
yp(x,h):= diff(y(x,h),x)$
ypp(x,h):=diff(yp(x,h),x)$

f(x,h):=''fullratsimp(''(ypp(x,h)/(1-yp(x,h)^2)))$ f(x,%pi/2);

g(x,h):=subst(sin(x),sqrt(1-cos(x)^2),f(x,h))$ g(x,%pi/2);

q(x,h):=subst(-sin(x)^2,cos(x)^2-1,g(x,h))$ q(x,%pi/2);

f(x,0);

G(x,h):=subst(cos(x),sqrt(1-sin(x)^2),f(x,h))$ G(x,0);

Q(x,h):=subst(cos(x)^2,sin(x)^2-1,G(x,h))$ Q(x,0);