Why infinity function on the TI Nspire CX if I cannot use it?

There is infinity on my TI nspire cx but I cannot use it. It occurs the message says "Unsupported feature This feature requires Computer Algebra System. Try Ti-Nspire CAS. I just don't understand why they put ∞ on the keyboard even can't use it. Can I upgrade to CAS with TI-nspire CX? or I can't use ∞ without using the TI-nspire CX CAS version?