let give f(x)= (1/(1+x^2 )) 1)prove that prove that
f^((n)) (x)=((p_n (x))/((1+x^2 )^(n+1) )) with p_n is a polynomial
2) prove that p_(n+1) (x)=(1+x^2 )p_n ^′ (x) −2(n+1)p_n (x)
3) calculate p_0 (x) ,p_1 (x) ,p_2 (x) ,p_3 (x) .
if the sum of first 5 terms of a G.P. is 155, sum of last 5 terms is 39680,first term is 5 and last term is 20480. find the number of terms of the sequence.