F of x

How it is used

Teachers and students say it all the time: 'f of x equals x squared', 'g of three', and 'f of g of x' for f(g(x)). The derivative f′(x) is read 'f prime of x' and the inverse f⁻¹(x) is read 'f inverse of x'.

Example sentences

1. If f of x equals 3x minus 1, what is f of 4?

2. Careful: the question asks for f of x plus h, not f of x plus f of h.

Common collocations

• f of x equals
• f prime of x
• f inverse of x
• f of g of x

Related terms

• functionA rule that takes each input from a set and gives exactly one output, for example f(x) = 2x + 1, which doubles a number and adds one.
• inverse functionA function that reverses the effect of another function, so that if f(2) = 7, the inverse of f takes 7 back to 2.
• derivativeA function that gives the rate of change of another function at each point, which is the slope of its graph there; the derivative of x² is 2x.
• plug inTo put a particular number in place of a variable in a formula or expression to see what result it gives; an informal word for 'substitute'.

More terms: Reading Maths Aloud

• equals
• squared
• to the power of
• divided by
• decimal point
• parentheses
• cubed