Lê Quốc Trần Anh Coordinator
17/05/2018 at 12:25-
a+b+c = 0
=> (a+b+c)2 = 0
=> a2 + b2 + c2 + 2ab + 2bc + 2ca = 0
We have: a2 + b2 + c2 \(\ge0\)
\(\Rightarrow2\left(ab+bc+ca\right)\le0\Leftrightarrow ab+bc+ca\le0\)
Lê Quốc Trần Anh selected this answer. -
Huy Toàn 8A (TL) 19/05/2018 at 02:02a + b + c = 0
=> (a + b + c)2 \(>_-\)0
<=> a2 + b2 + c2 + 2ab + 2cb + 2ac = 0
=> 2 (ab + bc + ca) \(< _-\) 0
Compact : ab + bc + ca \(< _-0\) -
Fc Alan Walker 18/05/2018 at 13:35a+b+c = 0
=> (a+b+c)2 = 0
=> a2 + b2 + c2 + 2ab + 2bc + 2ca = 0
We have: a2 + b2 + c2 ≥0
⇒2(ab+bc+ca)≤0⇔ab+bc+ca≤0