Need help with Edexcel A Level pure maths question

I was looking at this mark scheme while going over a past paper, and I don't understand how you're meant to get from r^6 = 1/8 (the point I got up to before getting stuck) to r = ±1/√2? I tried doing the sixth root of 1/8 on my calculator, but I just got 0.7071067812. Can anyone please explain? Let me know if I need to post the question for further context, not really sure if it's some contextual thing I overlooked or just a simplification thing

I wouldn’t do it by calcuator.
If you start from r^6 = 1/8, you should recognise that the cube root of 1/8 is 1/2, so taking cube roots of both sides:
r^2 = 1/2
Now if you take the square root, you should get the result in the MS - you have to recognise that the output can be positive or negative (hence the plus or minus sign)
Edit: 0.707… is also the approximate value of 1/root(2). The calculator only gives the positive square root, though.