(-3/4)+1/2;
(-3/4)+1/2;
1,1,2,3,3,4,4,7,( ),( )
1/2-(3/4-3/8), 1/2+1/4-1/6 , 2/3+(1/2+1/4),
1/2-(3/4-3/8),1/2+1/4-1/6 ,2/3+(1/2+1/4),
1、2、2、3、4、( )
(1)2×(-3)3-4×(-3)+15;
1/1 ,1/2 ,2/2,1/3,2/3,3/3 ,1/4,2/4,3/4,4/4 ,1/5,2/5----(找规律)
(-1/2)-(-1/3)-(+1/4)
1/2!+2/3!+3/4!+.+n/(n+1)!
1/4(1-3x/2)-1/3(2-x/4)=2
2\1+(3\1+3\2)+(4\1+4\2+4\3)+(5\1+5\2+5\3+5\4)+.+(40\1+40\2+.
计算 1/2-(1/3+2/3)+(1/4+2/4+3/4)-(1/5+2/5+3/5+4/5)+...-(1/21+2