Hard Reset HTC Nexus 9 WiFi

First method:

1. First, switch off the phone by using the Power button.
2. Afterwards press and hold Volum Down and Power buttons together for a couple of seconds.
3. You can release held keys when you see Bootloader Mode.
4. Then press Volume Down to select option "Factory reset", and press Power button to confirm.
5. Good job! The hard reset has just been perfomed!

Second method:

1. Turn on the phone by using the Power button. 
2. After pressing the Home button go to Settings and then to Security.
3. Select the Factory Data Reset and choose Reset Phone. 
4. Tap Erase Everything to confirm the whole operation. 
5. Wel done!

WARNING !
Hard Reset will erase all of your data
All described operations you are doing at your own risk.