Each state of the United States selects two senators to represent their states in the United States Senate. In 1913, the 17th Amendment[?] to the United States Constitution provided for the direct popular election of senators; prior to this, senators were selected by state legislatures.
... 2, the element 2a is zero and it is impossible to divide by it.)
The symbol
<math>\pm \sqrt {b^2-4ac}</math>
in the formula should be understood as ...