Which of the following principles was established by the United States Supreme Court in the 1803 Marbury v. Madison decision, making the Supreme Court a coequal branch of government?

While the concept of separation of powers is fundamental to the structure of the U.S. government, it was not specifically established by Marbury v. Madison. This principle divides government responsibilities among the three branches to prevent any one branch from gaining too much power, but the case focused primarily on the judiciary's authority to review legislative acts.

Republicanism refers to a political ideology centered around the governance of a state as a republic, with elected representatives and an emphasis on the rule of law. While integral to the foundation of the United States, this principle was not the focus of the Marbury v. Madison ruling, which dealt specifically with the judiciary's power.

Freedom of speech is a fundamental right protected by the First Amendment, but it was not a principle established by the Marbury v. Madison decision. This case was centered on the authority of the Supreme Court and the concept of judicial review, rather than issues relating to free expression or speech rights.