高一数学题

T2n = [ -b1^2 + b^2 ] + [ -b3^2 + b4^2 ] + …… + [ -(b2n-1)^2 + (b2n)^2 ]= ( b2 + b1 )( b2 - b1 ) + ( b4 + b3 )( b4 - b3 ) + …… + [ (b2n) + ( b2n-1) ][ (b2n) - (b2n-1) ]= b1 + b2 + …… + (b2n)；∴b2 - b1 = 1，b4 - b3 = 1，…… ，(b2n) - (b2n-1) = 1；∴ T2n是等差级数，公差d = 1；T2n =b1 + b2 + …… + (b2n) = [ b1 + (b2n) ]( 2n/2 ) = n[ b1 + (b2n) ] 。