And since the DIA and SPY own shares in mostly U.S. dividend paying companies, their dividends are mostly qualified. But some of the dividends in the SPY are not. You can look this up yourself using the tax data from the ETF provider.
Fractions are related to division because the top of the fraction is the numerator or the dividend of the fraction and the bottom of the fraction is the denominator or the divisor of the fraction. Minor edit?
The denominator in a fraction cannot be zero because division by zero is undefined. So we need to figure out what values of the variable(s) in the expression would make the denominator equal zero. These values cannot be included in the domain, so they're called excluded values.