let A be a $m \times n$ matrix
$$\|A\| _2 := sup_{x \in S^{n-1}, y \in S^{m-1}} <Ax,y>$$
let $r$ denotes first row of $A$ ,and $c$ denotes column of $A$. then $$\|A\| _2 \geq \|r\|_2 +\|c\|_2$$ where $\|\|_2$ denotes Euclidean norm , Is that true?
let A be a $m \times n$ matrix
$$\|A\| _2 := sup_{x \in S^{n-1}, y \in S^{m-1}} <Ax,y>$$
let $r$ denotes first row of $A$ ,and $c$ denotes column of $A$. then $$\|A\| _2 \geq \|r\|_2 +\|c\|_2$$ where $\|\|_2$ denotes Euclidean norm , Is that true?
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If $A$ is the matrix $\pmatrix{0 & 0 \\ 0 & 1}$, then the first row and first column have 2-norm $0$, while the operator norm is clearly $1$ (attained by $\pmatrix{0 \\ 1}$).