Recent content by Crystals

Thank you guys for your reply. I did the (2) derivative by Ray Vickson and this is the draft solution I got. Is this correct to say that the derivatives both sides of the geometric sum , with respect of x is: \frac{d}{dx}\frac{1-x^{n+1}}{1-x} =\frac{x^{n}(n(x-1)-1)+1}{(x-1)(x-1)}...

Can someone guide me with the steps to differentiate a geometric sum, x? ^{n}_{i=0}\sumx^{i}=\frac{1-x^{n+i}}{1-x} If I'm not wrong, the summation means: = x^0 + x^1 + x^2 + x^3 + ... + n^i Problem is: I have basic knowledge on differentiating a normal numbers but how do I apply...