1, Chứng minh rằng: a, a\(^2\) + b\(^2\) + 1 \(\ge\) ab + a + b .
b, a\(^2\) + b\(^2\) + c\(^2\) \(\ge\) a(b + c) .
2, Chứng minh rằng: Với mọi a, b, c thì ta có:
a, a\(^2\) + b\(^2\) + c\(^2\) +3 \(\ge\) 2(a+b+c).
b, (a+b+c)\(^2\) \(\le\) 3 (a\(^2\) + b\(^2\) +c\(^2\)).
c, 8(a\(^4\) +b\(^4\)) \(\ge\) (a+b)\(^4\).