Practice problem
What's the radius of convergence of cos(z)=1−z22!+z44!−⋯\cos(z) = 1 - \frac{z^2}{2!} + \frac{z^4}{4!} - \cdotscos(z)=1−2!z2+4!z4−⋯? Note zzz is complex.
∣z∣<1|z| < 1∣z∣<1
All positive zzz
∣z∣<e|z| < e∣z∣<e
All zzz
Type a concept, like “slope” or “photosynthesis”.