a)
a_n=(-1)^{n+1}*\frac{4-n^2}{n+1}
a_1=(-1)^{1+1}*\frac{4-1^2}{1+1}=(-1)^2*\frac{3}{2}=1*1,5=1,5
a_2=(-1)^{2+1}*\frac{4-2^2}{2+1}=(-1)^2*\frac{0}{3}=1*0=0
a_5=(-1)^{5+1}*\frac{4-5^2}{5+1}=(-1)^6*\frac{-21}{6}=1*(-\frac{21}{6})=-\frac{21}{6}=-\frac{7}{3}=-2\frac{1}{3}
b)
b_n=(\frac{n-1}{n+1})^{2-n}
b_1=(\frac{1-1}{1+1})^{2-1}=(\frac{0}{2})^1=0^1=0
b_2=(\frac{2-1}{2+1})^{2-2}=(\frac{1}{3})^0=1
b_5=(\frac{5-1}{5+1})^{2-5}=(\frac{4}{6})^{-3}=(\frac{6}{4})^6=(\frac{3}{2})^6=1,5^6
c)
c_n=2log\ n+log4
c_1=2log 1+log4=log1^2+log4=log(1*4)=log4
c_2=2log2+log4=log2^2+log4=log4+log4=2log4=log4^2=log16
c_5=2log5+log4=log5^2+log4=log(25*4)=log100=log10^2=2