Let the function f(x)be continuous on the closed interval a,b],differentiable in the openinterval (a,b),and f"(x)>0.If the limit:limf(2x -a)exists,prove:x-a+x-a(①)In(a,b),f(x)>0;b2-a2-25()There exists point in (a,b),such thatf(x)dxf()(i)There is a point n in(a,b)which is different fromin(l,so(n)(6-2)-2兰x)d.