求和:1/1x4+1/4x7+···+1/(3n-2)x(3n+1)要精准一点的,快~~~谢啦

求和:1/1x4+1/4x7+···+1/(3n-2)x(3n+1)要精准一点的,快~~~谢啦 1/1x4+1/4x7+…+1/97x100 x1-x2+x3=1x2-x3+x4=21若x1,x2,x3,x4,x5满足方程组 x3-x4+x5=3x4-x5+x1=4x5-x1+x2=5求x2 x3 x4的值2已知 x1+x4+x6+x7=39 x2+x4+x5+x7=49 x3+x5+x6+x7=41 x4+x7=13 x5+x7=14 x6+x7=9 x1+x2+x3+x4+x5+x6+x7=9求x7的值若x1,x2,x3,x4,x5满足方程组 x1-x 1/1x4+1/4x7+1/7x10+...+1/73x76=? 急啊······ x8+x7+x6 +x5+x4+x3+x2+x+1因式分解 x8+x7+x6+x5+x4+x3+x2+x+1因式分解 100x( 3/1x4 + 3/4x7 +3/7x10 +.3/97x100)=?注：1x4、4x7、7x10等均为分母的大小 1/1x4+1/4x7+1/7x10+1/10x13+1/13X16 简便 计算：1/（1x4）+1/（4x7）+1/(7x10)…+1/(298x301) 计算1/1x4+1/4x7+1/7x10+***+1/2007x2010 1/1x4+1/4x7+1/7x10+……+1/2005x2008佼佼我 1/1X4+1/4X7+1/7X10+...+1/100X103= 1/1x4+1/4x7+1/7x10+……+1/97x100SOS!SOS! 1/(1x4)+1/(4x7)+1/(7x10)+...+1/(91x94) 1/1X4+1/4X7+1/7X10+.+1/2002X2005=?有规律的 1/1x4+1/4x7+1/7x10+……+1/2005x2008 1X4/1+4X7/1+7X10/1+…+2005X2008/1=? 1/1x4 +1/4x7+1/7x10+.+1/100x103 急用啊