Q76. "Is the United States a constitutional republic? Is one of the purposes of a constitutional republic to protect the rights of minorities from the tyranny of the majority?"
A. The United States is a federal republic and a constitutional representative democracy.
The "federal" part is one of three basic types of organization of power — unitary, confederal, and federal. Most nations are unitary in nature (local government with a powerful national government). There are no confederacies that I know of at this time (the U.S., under the Articles of Confederation was one; Germany and Switzerland have also had confederate systems in the past). Federal systems are common among large nations where several levels of government are needed. Australia, Canada, and Brazil are federal as well. Federations do not always work, such as in the case of the United Arab Republic.
The "republic" implies that we have a strong head of state (the President) and elected officials representing the people.
The "constitutional" part means that we have a constitution, which is pretty obvious, considering this site. Finally, the "representative democracy" part means that the people elect representatives to take care of legislative matters. Originally, the only part of the government that fit this description was the House of Representatives. Today, the Senate does, too, and in current practice, so does the Electoral College.
The mere fact that a nation has a constitution, is a federation, or is a republic, does not imply that minorities are fairly treated. It is the content of that constitution, and the values of that federation and/or republic that protects the rights of minorities.
Note that a democracy, in the true sense of the word, does not protect the minority — majority rules.