Tìm x biếta, ( x + 1 ) + ( x + 4 ) + ( x + 7 ) + .... + ( x + 28 ) = 155b, 1 + \(\frac{1}{3}\) + \(\frac{1}{6}\)+ \(\frac{1}{10}\) + ..... + \(\frac{2}{x.\left(x+1\right)}\)= \(1\frac{2009}{2010}\)c, \(\left(\frac{2}{11.13}+\frac{2}{13.15}+\frac{2}{15.17}+....+\frac{2}{19.21}\right)\) . 462 - x =...
Đọc tiếp
Tìm x biết
a, ( x + 1 ) + ( x + 4 ) + ( x + 7 ) + .... + ( x + 28 ) = 155
b, 1 + \(\frac{1}{3}\) + \(\frac{1}{6}\)+ \(\frac{1}{10}\) + ..... + \(\frac{2}{x.\left(x+1\right)}\)= \(1\frac{2009}{2010}\)
c, \(\left(\frac{2}{11.13}+\frac{2}{13.15}+\frac{2}{15.17}+....+\frac{2}{19.21}\right)\) . 462 - x = 19
a, (x+1)+(x+4)+(x+7)+...+(x+28)=155
=>x.10+(1+4+7+...+28) =155
=> x.10+145 =155
=> x.10 = 155-145
=> x.10 = 10
=> x =10:10
=> x =1
Vậy x= 1