Cita APA (7th ed.)

Freudenthal, H. (1967). Mathematics observed. McGraw-Hill Book Co., Inc.

Cita Chicago (17th ed.)

Freudenthal, Hans. Mathematics Observed. New York: McGraw-Hill Book Co., Inc, 1967.

Cita MLA (9th ed.)

Freudenthal, Hans. Mathematics Observed. McGraw-Hill Book Co., Inc, 1967.