tìm a biết a+a*2+a*3+a*4+...+a*49+a*50=12750
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![](https://rs.olm.vn/images/avt/0.png?1311)
![](https://rs.olm.vn/images/avt/0.png?1311)
![](https://rs.olm.vn/images/avt/0.png?1311)
a ( 1+2+3+4+...+ 49+50 ) = 12750
a x 1275 = 12750
a = 10
![](https://rs.olm.vn/images/avt/0.png?1311)
![](https://rs.olm.vn/images/avt/0.png?1311)
=> a . ( 1 + 2 + 3 + .... + 49 + 50 ) = 12750
=> a . { [ 50.( 50 + 1 ) ] : 2 } = 12750
=> a. ( 2550 : 2 ) = 12750
=> a. 1275 = 12750
=> a = 12750 : 1275
=> a = 10
![](https://rs.olm.vn/images/avt/0.png?1311)
a*(1+2+3+.......................+50)=12750
a*1275=12750
a=12750:1275
a=10
a + a × 2 + a × 3 + a × 4 + … + a × 49 + a × 50 = 12750
a x (1 + 2 + 3 + ... + 50) = 12750
a x 1275 = 12750
a = 12750 : 1275
a = 10
![](https://rs.olm.vn/images/avt/0.png?1311)
![](https://rs.olm.vn/images/avt/0.png?1311)
=> a.( 1 + 2 + 3 + .... + 49 + 50 ) = 12750
=> a.{ [ 50.( 50 + 1 ) ] : 2 } = 12750
=> a.[ 2550 : 2 ] = 12750
=> a.1275 = 12750
=> a = 12750 : 1275
=> a = 10
a + a x 2 + a x 3 + a x 4 +.....+ a x 49 + a x 50= 12750
a x 1 + a x 2 + a x 3 + a x 4 +........+ a x 49 + a x 50 =12750
a x ( 1 + 2 + 3 + 4 + ......+ 49 + 50 ) = 12750
a x ( 50 + 1 ) x 50 :2 =12750
a x 1275 = 12750
a = 12750 : 1275
a = 10
duyệt nha
a + a x 2 + a x 3 + a x 4 + ... + a x 49 + a x 50 = 12750
a x ( 1 + 2 + 3 + 4 + ..+ 49 + 50 ) = 12750
a x 1275 = 12750
a = 12750 : 1275
a = 10
Vậy a = 10
Giải:
Ta có:a*1+a*2..................a*50=12750
Vậy a*(1+2+3+..................+50)=12750
a=12750:(1+2+3+..................+50)
a=12750:1275
a=10