an=2n
1/an=1/(2n)
1/an^2=1/(2n)^2
1/a1^2+1/a2^2+1/a3^2+.+1/an^2
=1/(4*1^2)+1/(4*2^2)+1/(4*3^2)+.+1/(4*n^2)
=1/4*(1/1^2+1/2^2+1/3^2+.+1/n^2)
an=2n
1/an=1/(2n)
1/an^2=1/(2n)^2
1/a1^2+1/a2^2+1/a3^2+.+1/an^2
=1/(4*1^2)+1/(4*2^2)+1/(4*3^2)+.+1/(4*n^2)
=1/4*(1/1^2+1/2^2+1/3^2+.+1/n^2)