=(- 1)^(n- 1)*4n/(2n- 1)*(2n+ 1)
=(- 1)^(n- 1)*[((2n+ 1)+(2n- 1))/(2n- 1)*(2n+ 1)]
=(- 1)^(n- 1)*[(2n+ 1)/(2n- 1)*(2n+ 1)+(2n- 1)/(2n- 1)*(2n+ 1)]
=(- 1)^(n- 1)*[ 1/(2n- 1)+ 1/(2n+ 1)]
Diagonal lines AC and BD intersect at e,
According to cosine theorem, cos
Similarly, cos
¡ßcos( 180-& lt£» BCD)=-cos & lt£» BCD =