APA (7th ed.) Citation

Polya, G. (1990). How to solve it: A new aspect of mathematical method (2nd ed.). Penguin Books.

Chicago Style (17th ed.) Citation

Polya, George. How to Solve It: A New Aspect of Mathematical Method. 2nd ed. London: Penguin Books, 1990.

MLA (8th ed.) Citation

Polya, George. How to Solve It: A New Aspect of Mathematical Method. 2nd ed. Penguin Books, 1990.

Warning: These citations may not always be 100% accurate.