Question: How to plot two functions of two variables?

How plot two functions of two variables to (2-dimension)?

restart;
approximate := exp(-2*t)+x*exp(-2*t)+(1/2)*exp(-2*t)*x^2+(1/6)*exp(-2*t)*x^3+(1/24)*exp(-2*t)*x^4+(1/120)*exp(-2*t)*x^5+(1/720)*exp(-2*t)*x^6+(1/5040)*exp(-2*t)*x^7+(1/40320)*exp(-2*t)*x^8+(1/362880)*exp(-2*t)*x^9+(1/3628800)*exp(-2*t)*x^10+(1/39916800)*exp(-2*t)*x^11+(1/479001600)*exp(-2*t)*x^12+(1/6227020800)*exp(-2*t)*x^13+(1/87178291200)*exp(-2*t)*x^14+(1/1307674368000)*exp(-2*t)*x^15+(1/20922789888000)*exp(-2*t)*x^16+(1/355687428096000)*exp(-2*t)*x^17+(1/6402373705728000)*exp(-2*t)*x^18+(1/121645100408832000)*exp(-2*t)*x^19+(1/2432902008176640000)*exp(-2*t)*x^20+(1/51090942171709440000)*exp(-2*t)*x^21;
apr := unapply(approximate, x, t);
Exact := (x, t)-> exp(x-2*t) ;
plot3d(exp(x-2*t)-approximate, x = 0 .. 5, t = 0 .. 5);

plot.mw