1/42=1/?-1/?
1/42=1/?-1/?
1/12+1/20+1/30+1/42=?
1/20+1/30+1/42+1/56=
1/2+1/6+1/12+1\20+1/30+1/42+.+1/9900=?
1/2+1/6+1/12+1/20+1/30+1/42+1/56=?
1/12+1/20+1/30+1/42+1/56+1/72+1/90=?
2/1+6/1+12/1+20/1+30/1+42/1+56/1=
2/1+6/1+12/1+20/1+30/1+42/1+56/1=?
1/2+1/6+1/12+1/20+1/30+1/42+1/56=
1+1/2+1/6+1/12+1/20+1/30+1/42=?
(1+0.8%)x+(1+1.1%)×(42-x)=(1+1%)×42
42x(8/1+24/1+48/1+80/1+120/1+168/1)=?