V := Pi*r^2*h; r0 := 80*cm: h0 := 150*cm: Answer1 := 'diff(V,r)'*'diff(r,t)' + 'diff(V,h)'*'diff(h,t)'; answer1 := diff(V,r)*(-1.2*cm/s) + diff(V,h)*(3*cm/s); answ1 := subs({r=r0,h=h0},answer1); ans1 := evalf(answ1); # R:=sqrt(a^2+b^2);a0:=0.3*km;b0:=0.4*km;da2dt:=-90*km/h;db2dt:=-80*km/h; ex1 := diff(R,a)*da2dt + diff(R,b)*db2dt; answer2 := simplify(evalf( subs({a=a0,b=b0},ex1) )); assume(km > 0): answer2;