# I Cross product?

#### Dubz

The problem is a PDE
uxx+uyy= 0 in ℝx(0,∞)

what does this mean ℝx(0,∞) ?
Came across it in my math book, and I have not idea what to google to find this.

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#### fresh_42

Mentor
2018 Award
The problem is a PDE
uxx+uyy= 0 in ℝx(0,∞)

what does this mean ℝx(0,∞) ?
Came across it in my math book, and I have not idea what to google to find this.
It probably means the set $\{(x,y) \in \mathbb{R}^2\,\vert \,y>0\} = \mathbb{R} \times \mathbb{R}_+\,.$

#### protonsarecool

To answer your google question, it is called the Cartesian product. As fresh said, it is just the set of ordered tuples.

"Cross product?"

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