a,x+x2+x3+....+x9=459-9
<=>x(1+2+3+...+9)=450
<=>x45=450
<=>x=10
b ,thì tương tự nhé b
28 giây trước (15:57)
Tìm x , biết
a)x+2x+3x+...+9x=459 - 9
45x = 450
x= 10
---------
b)x+(x+1)+(x+2)+...+(x+30)=1240
31x + (1 +2 + 3 ....+ 30 ) =1240
31x + 456 = 1240
31x = 784
x= 784/31
a)\(x+2x+3x+...+9x=459-9\)
\(x+2x+3x+...+9x=450\)
\(x\left(1+2+3+...+9\right)=450\)
\(45x=450\)
\(x=450\div45\)
\(x=10\)
b)\(x+\left(x+1\right)+\left(x+2\right)+...+\left(x+30\right)=1240\)
\(x+x+1+x+2+...+x+30=1240\)
\(\left(x+x+x+...+x\right)+\left(1+2+3+...+30\right)=1240\)
\(31x+465=1240\)
\(31x=1240-465\)
\(31x=775\)
\(x=775\div31\)
\(x=25\)
