x=[-2:0.01:4];
y=3*x.^3-26*x+10;
yd=9*x.^2-26;
ydd=18*x;

% plot(x,y,'-b')
% plot(x,yd,'--r')
% plot(x,ydd,':k')


plot(x,y,'-b',x,yd,'--r',x,ydd,':k')
grid on


figure,
subplot(221), plot(x,y,'r')
grid on
subplot(222), plot(x,yd,'b')
grid on
subplot(223), plot(x,ydd,'k')
grid on
subplot(224), plot(x,y,'r',x,yd,'b',x,ydd,'k')
grid on