Find out whether or not the indicated product satisfies the conditions for an inner product in the given vector space.
1) In R^2, let <(x1,x2),(y1,y2)> = x1*y1 - x2*y2
2) In R^2, let <(x1,x2),(y1,y2)> = x1^2*y1 + x2*y2
3) In R^2, let <(x1,x2),(y1,y2)> = x1*y2
4) In R^3, let <(x1,x2,x3),(y1,y2,y3)> = x1+y1