So ab≤8,
And because a > 0 and b > 0, ab>0.
So 0
a+b = √( a+b)2 =√a2+B2+2ab =√ 16+2ab
Because 0
So 4 < √ 16+2ab≤4√2
All four.
√ indicates the root sign (this will do. I forgot to think about it. Sorry)