SEGGER_RTT_printf is not working

[nordicbeginner]

hello there, i am using sdk11, i am using uart example. i am using nrf51 dk SEGGER_RTT_WriteString is working. but SEGGER_RTT_printf is not working.main.c

i have seen this link devzone.nordicsemi.com/.../

[nordicbeginner]

._build\nrf51422_xxac.axf: Error: L6218E: Undefined symbol SEGGER_RTT_printf (referred from main.o).