question is : with(combinat): sum(numbcomb(80, x)*numbcomb(100, 27-x), x = 1 .. 27)

this cannot get the answer rather than add

of course the following is ok

tot := 0; for x to 27 do tot := tot+numbcomb(80, x)*numbcomb(100, 27-x) end do: tot

question1:

plot(2/(3*x)+x, x = -5 .. 5)

Though this is ok ：plot(2/(3*x)+x, x = -5 .. 5, y = -5 .. 5)

but ... lazy to set range of y axis at the very start.

 question2：

how to plot more graph on different invertals  one time.

for example the intarvals [-5,5],[-1,1],[0,1]

(∑)a[ijk](t)(x^(j))^((k))+b^(j)(t)=0,i=1,..,n.

click enter,and the font will be automatical converted to Times New Roman

but with error information about my subscript (j,k)

s1 := series(sin(x), x, 6)

c1 := series(cos(x), x, 6)

e := exp(1)

e1 := series(e^x, x, 6)

how to make s1+c1 =  e1's form,but x-(1/6)*x^3+(1/120)*x^5+O(x^6)+(1-(1/2)*x^2+(1/24)*x^4+O(x^6))

I mean when typing polynomials, convert the 2x4 to 2x^4,,,

for 4 is in the right

and sometimes I'm a little lazy(?).

...