Easy question

[ijabbott]

The result of (-1)^(4/5) will depend on whether or not you have the "Allow complex output from real input" option turned on or off in the settings. If turned off, you will get the real result -1. If turned on, you will get the complex result -0.809016994375+0.587785252292*i. Also, I think the CAS mode always approximates to the complex result.

Since -1 is e^(i*π), (-1)^(4/5) is (e^(i*π))^(4/5), which is e^(i*π*4/5) in exponential form, or 1∡(π*4/5) in polar form (radians mode), or cos(π*4/5)+sin(π*4/5)*i in rectangular form (radians mode).

In CAS mode, pow2exp((-1)^(4/5)) produces e^((4/5)*i*π).