My brother said I did this wrong can someone check this for me please

Question

X Y-1 = sum(x)+ (y-1)=(X+y-1) diff(x)-(y-1)=(x+y+1)
Product (x) (x-1) = (xy-1) = (xy-1)

Answer 1

sum (x)+(y-1) = x+y-1
diff (x)-(y-1) = x-y+1
prod (x)*(y-1) = xy - x