Toán Lớp 7: Tìm x biết:

Question

Toán Lớp 7:  Tìm x biết:                                                                                                                                                                         a. (5x-1,45)/6 + (5x-1,45)/7 + (5x-1,45)/8 = (5x -1,45)/9 + (5x-1,45)/10                                                                b*. (x+5)/2011 + (x+4)/2012 = (x+3)/2013 + (x+2)/2014

tuyetnhungthu · Answer

Giải đáp:       Lời giải và giải thích chi tiết:          a    ,       a,                5    x    &minus;    1    ,    45       6       +        5    x    &minus;    1    ,    45       7       +        5    x    &minus;    1    ,    45       8       =        5    x    &minus;    1    ,    45       9       +        5    x    &minus;    1    ,    45       10          5x-1,456+5x-1,457+5x-1,458=5x-1,459+5x-1,4510               &rarr;        5    x    &minus;    1    ,    45       6       +        5    x    &minus;    1    ,    45       7       +        5    x    &minus;    1    ,    45       8       &minus;        5    x    &minus;    1    ,    45       9               &minus;        5    x    &minus;    1    ,    45       10       =    0          &rarr;5x-1,456+5x-1,457+5x-1,458-5x-1,459-5x-1,4510=0            &rarr;     (    5    x    &minus;    1    ,    45    )      (       1      6       +       1      7       +       1      8       &minus;       1      9       &minus;       1      10       )     =    0       &rarr;(5x-1,45)(16+17+18-19-110)=0            &rarr;    5    x    &minus;    1    ,    45    =    0       &rarr;5x-1,45=0     (Do             1      6            +       1      7       +       1      8       &minus;       1      9       &minus;       1      10       &ne;    0       16 +17+18-19-110&ne;0  )          &rarr;    5    x    =    1    ,    45       &rarr;5x=1,45            &rarr;    x    =       29      100          &rarr;x=29100     Vậy          x    =       29      100          x=29100                       b    ,       b,                x    +    5       2011       +        x    +    4       2012       =        x    +    3       2013       +        x    +    2       2014          x+52011+x+42012=x+32013+x+22014            &rarr;        x    +    5       2011       +        x    +    4       2012       +    2    =        x    +    3       2013       +        x    +    2       2014       +    2       &rarr;x+52011+x+42012+2=x+32013+x+22014+2            &rarr;     (        x    +    5       2011       +    1    )     +     (        x    +    4       2012       +    1    )     =     (        x    +    3       2013       +    1    )     +     (        x    +    2       2014       +    1    )        &rarr;(x+52011+1)+(x+42012+1)=(x+32013+1)+(x+22014+1)               &rarr;     (        x    +    5       2011       +       2011      2011       )     +     (        x    +    4       2012       +       2012      2012       )     =     (        x    +    3       2013       +       2013      2013       )             +     (        x    +    2       2014       +       2014      2014       )           &rarr;(x+52011+20112011)+(x+42012+20122012)=(x+32013+20132013)+(x+22014+20142014)            &rarr;        x    +    2016       2011       +        x    +    2016       2012       =        x    +    2016       2013       +        x    +    2016       2014          &rarr;x+20162011+x+20162012=x+20162013+x+20162014            &rarr;        x    +    2016       2011       +        x    +    2016       2012       &minus;        x    +    2016       2013       &minus;        x    +    2016       2014       =    0       &rarr;x+20162011+x+20162012-x+20162013-x+20162014=0            &rarr;     (    x    +    2016    )      (       1      2011       +       1      2012       &minus;       1      2013       &minus;       1      2014       )     =    0       &rarr;(x+2016)(12011+12012-12013-12014)=0            &rarr;    x    +    2016    =    0       &rarr;x+2016=0     (Do             1      2011       +       1      2012       &minus;       1      2013       &minus;       1      2014       &ne;    0       12011+12012-12013-12014&ne;0  )          &rarr;    x    =    &minus;    2016       &rarr;x=-2016     Vậy          x    =    &minus;    2016

hiennhi98 · Answer

$  $   a,   (5x-1,45)/6 + (5x-1,45)/7 + (5x-1,45)/8 = (5x-1,45)/9 + (5x-1,45)/10   -> (5x-1,45)/6 + (5x-1,45)/7 + (5x-1,45)/8 - (5x-1,45)/9 - (5x-1,45)/10=0   -> (5x-1,45) (1/6 + 1/7 + 1/8 - 1/9 - 1/10)=0   ->5x-1,45=0 (Do 1/6  +1/7 +1/8 - 1/9-1/10  ne 0)   ->5x=1,45   ->x=29/100   Vậy x=29/100   $  $   b,   (x+5)/2011 + (x+4)/2012 = (x+3)/2013 + (x+2)/2014   -> (x+5)/2011 + (x+4)/2012 +2 = (x+3)/2013 + (x+2)/2014 + 2   -> ( (x+5)/2011 +1)+( (x+4)/2012 +1) = ( (x+3)/2013 +1) + ( (x+2)/2014 +1)   -> ( (x+5)/2011 +2011/2011)+( (x+4)/2012 +2012/2012) = ( (x+3)/2013+2013/2013)+( ( x+2)/2014+2014/2014)   -> (x+2016)/2011 + (x+ 2016)/2012 = (x+2016)/2013 + ( x+2016)/2014   -> (x+2016)/2011 + (x+ 2016)/2012 - (x+2016)/2013 - (x+2016)/2014=0   -> (x+2016)(1/2011 +1/2012-1/2013-1/2014)=0   ->x+2016=0 (Do 1/2011 +1/2012-1/2013-1/2014  ne 0)   ->x=-2016   Vậy x=-2016