The image shows the following (using the appropriate fonts, where the maths is centred, and the spacing is better):
a_{i} x_{i} = b_{i}
for all i=1,...,n

The for all symbol, an upside-down A, is used in place of "for all".
If your browser can't render the above this reads:
a subscript i x subscript i = b subscript i for all
i = 1,...,n