How does this part of the constitution uphold the principles of a representative democracy?

Answer

The Seventh Amendment of the U.S Constitution allows for application of the principle of representative democracy.

Explanation

A representative democracy is  a governing system in a country that allows its citizens to vote for those representing them in congress for passing laws. This system works where there is: equal opportunity during competition that select leaders, free communication and a strong belief by voters in choosing candidates. The foundations of representative democracy are equal chances to vote, citizen inclusion, agenda controlled by citizens and effective participation of citizens.

the american revolution was by the middle and upper class, and the french was by the lower and middle class.

congress also has implied powers, which derive from the necessary and proper clause of the constitution and permit congress "to make all laws which shall be necessary and proper for carrying into execution the foregoing powers, and all other powers vested by this constitution in the government of the united states.