a) Prove that 0=inf{∣x2+y3+y5∣x,y,z∈Z,x2+y2+z2>0}b) Prove that there exist three positive rational numbers a,b,c such that the expression E(x,y,z):=xa+yb+zc vanishes for infinitely many integer triples (x,y,z), but it doesn´t get arbitrarily close to 0.