(x+2)+(x+12)(x+42)+(x+47)=655
(x+x+x+x) + (2+12+42+47) =655
4x + 103 =655
4x =552
x =138
x+(x+1)+(x+2)+(x+3)+...+(x+2009)=2009⋅2010
(x+x+x+...+x+x)+(1+2+3+...+2009)=2009.2010 (có 2010 số hạng x)
2010x +(2009+1).2009:2 =2009.2010
2010x +2010.2009:2 =2009.2010
2010x =(2009.2010)-(2010.2009:2)
2010x =(2009.2010)(1-\(\frac{1}{2}\))
2010x =2009.2010.\(\frac{1}{2}\)
x =2009.\(\frac{1}{2}\)
x =\(\frac{2009}{2}\)