a/ Thay x=1 vao phuong trinh:
3.1^2+7.1+m=0
<=> 10+m=0
<=> m=-10
Vay m=-10
b/ Thay x=1/3 vao phuong trinh:
15.(1/3)^2+m/3-1=0
<=> m/3+2/3=0
<=>m=-2
Vay m=-2
c/ Thay x=-1 vao phuong trinh:
(-1)^2-2(3m+1).(-1)+2m^2-2m-5=0
<=> 2m^2+4m-2=0
<=>m^2+2m-1=0
<=> (m+1)^2-2=0
<=>m+1=sprt(2) hay m+1=-sprt(2)
<=>m=-1+sqrt(2) hay m=-1-sqrt(2)