i) P'(z)=5z^4+3az^2+b
=5[z^4+3az^2/5+b/5]
=5[(z^2+3a/10)^2+b/5-9a^2/100]
>=5[9a^2/100+b/5-9a^2/100]
=5(b/5)=b
>0
ie. P'(z)>0 Hence, P(z) is increasing function to infinity since its a poly.
Now, P(0)=-c <0. Thus, P(z) has only one real root as it can only cross x-axis once.
ii)If...