1×9

1×9 denotes the product of 1 and 9, commonly read as one times nine. In standard arithmetic, 1×9 equals 9.

The expression highlights the multiplicative identity: multiplying any number by 1 yields the same number, so 1×9 and 9×1 both equal 9.

Geometrically, 1×9 can describe a rectangle with sides 1 and 9. The area is 9 square units, and the perimeter is 2×(1+9) = 20 units.

In linear algebra, a 1×9 matrix is a row vector with nine components; its transpose is a 9×1 column vector. Multiplying a 1×9 matrix by a 9×1 matrix yields a 1×1 scalar, equal to the dot product of the row and column.

In numeral systems, the digit 9 is valid only in bases greater than 9; in bases with fewer digits, 9 would be represented differently. Nevertheless, the value of the decimal expression 1×9 is 9.