Solve [{2x - 2y +  z -  w == 7,
    - x + 4y - 5z + 3w == 1,
      x +  y -  z +  w == 4,
    -4x + 2y +  z - 2w == 6},{x,y,z,w}]

Factor[x^3-21x+20]

Solve[{x^3-21x+20==0},{x}]

Integrate[e^(-x^2),{x,1,10}]

Sum[(-1)^n/(n^2),{n,1,Infinity}]

Plot[x^2+2x+3,{x,-5,5}]

Plot[Cos[2x],{x,-3,3}]

Plot[Sin[1/x],{x,-0.1,0.1}]

Plot3D[x^2+y^2,{x,-2,2},{y,-2, 2}]

Plot3D[x^2−y^2 + 2 x y ^2+1,{x,-2,2},{y,-2, 2}]