ta có
[tex]m^{2}+n^{2}+p^{2}+q^{2}+1\geq m\left ( n+p+q+1 \right )\left ( 1 \right )[/tex]
[tex]\Leftrightarrow m^{2}+n^{2}+p^{2}+q^{2}+1\geq mn+mp+mq+m[/tex]
[tex]\Leftrightarrow m^{2}+n^{2}+p^{2}+q^{2}+p^{2}+q^{2}+1-mn-mp-mq-m\geq 0[/tex]
[tex]\Leftrightarrow \left ( \frac{m^{2}}{4}-m+1 \right )+\left ( \frac{m^{2}}{4}-mn+n^{2} \right )+\left ( \frac{m^{2}}{4}-mp+p^{2} \right )+\left ( \frac{m^{2}}{4}-mq+q^{2} \right )\geq 0[/tex]
[tex]\Leftrightarrow \left ( \frac{m}{2}-1 \right )^{2}+\left ( \frac{m}{2}-n \right )^{2}+\left ( \frac{m}{2}-p \right )\left ( \frac{m}{2}-q \right )\geq 0[/tex] [2]
=>bpt 2 luôn đúng
=>bpt 1 đúng
dấu"=" xảy ra khi
m/2 -1=0
m/2 -p =0
m/2 -n =0
m/2 -q =0
=> m=2 ; n=p=q=1