I would like some assistance with the following calculus

12. Find the stationary points and determine if each stationary point gives a local/global maximum or local/global minimum, neither, or "can't tell" (i) f(x,,x2,x,)=x+2.x}+x3+x,x2-2.x, -7.x,+12 (ii) f(x,,X2.x,)=2x, - x, +10x2 -x, + 3x, -x3 (iii) f(x,,X2,x;)=3-x -2x, - 3x3 -2x,X2 - 2.xx, (iv) f (x,y) = x4+ x2 - 6xy + 3y2 (V ) f (x,y) = xyl + xy- xy (vi) f(x,y) = 3x4+ 3xly -y3 (vii) f(x1,X2, X3, X4) = 24x, + 32x2 + 48x3 + 72x4 - (x] + x} + 2x} + 3x]) 2 13. Find the stationary points and determine if each stationary point gives a local maximum or local minimum or neither. (i) f(x,,XX,)me--21-13-245 (ii) f( x, , x, .x,) -x +x,+x,+2xx,x, (iii) f(x,,x,.x,)= -x, +15x, -48.x, +2x, -3x, + fe" di (iv) f(x,y,z) = x2 + 6xy + y2 - 3yz + 4z2 - 10x - 5y - 21z (v) f (x, y,z) = (x2 + 2y2 + 3z?)e-(x2+y?+2?)