Question

数学计算题(设元法)(1/11+1/12+1/13+1/14+1/15)*(1/12+1/13+1/14+1/15+1/

Answer 1

设t=1/12+1/13+1/14+1/15,

则原式=(1/11+1/t)*(1/t+1/16)-(1/11+1/t+1/16)*t=t/11+t^2+1/(11*16)+t/16-t/11-t^2-t/16

=1/(11*16)