If f(y)=y1-y2,g(y)=y1+y2,then (fog)(y) is equal to
y1-y2
y1+y2
y
1-y21-y2
f(y)=y1-y2,g(y)=y1+y2and fogy=fgy=fy1+y2=y1+y21-y21+y2=y1+y211+y2=y