Chapter 4 - Graphs of the Circular Functions - Section 4.2 Translations of the Graphs of the Sine and Cosine Functions - 4.2 Exercises - Page 156: 19

right

(Refer to the graph below.) When translated $\frac{\pi}{2}$ units to the right, the graph of the cosine function (the red one) will coincide with the graph of the sine function (the blue one). Thus, the missing word in the given statement is $\bf\text{right}$.