Bài 15:
$f(-2)=f(2)$
$⇒3.(-2)^2+2.(-2)m-5=3.2^2+2.2m-5$
$⇒3.4-2m-5=3.4+4m-5$
$⇒12-2m-5=12+4m-5$
$⇒-2m-4m=12-5-12+5$
$⇒-6m=0$
$⇒m=0$
Bài 16:
$P(-1)=(-1)^3-3m.(-1)+m^2=-1+3m+m^2$
$Q(2)=2^2+(3m+2).2+m^2=4+6m+4+m^2=8+6m+m^2$
$P(-1)=Q(2)$
$⇒-1+3m+m^2=8+6m+m^2$
$⇒m^2+3m-6m-m^2=8+1$
$⇒-3m=9$
$⇒m=-3$