Toán Lớp 6: tìm số nguyên x, biết: a) 1^2021+99 (5-x)=94-(-321)+279, b) 72:(x-2)^2=8, c) 75-5 (x-3)^3=700

Question

Toán Lớp 6:  tìm số nguyên x, biết: a) 1^2021+99 (5-x)=94-(-321)+279, b) 72:(x-2)^2=8, c) 75-5 (x-3)^3=700

ngoclandiep · Answer

Giải đáp:     a) 1^2021+99 (5-x)=94-(-321)+279    => 1+99(5-x)= 94+321+279   => 100(5-x)= 694   => 5-x= 694:100   => 5-x=6,94   => x=5-6,94   => x=-1,94   => x&isin;&empty;       Vậy kh&ocirc;ng c&oacute; x thỏa m&atilde;n.       b) 72:(x-2)^2=8   => (x-2)^2=72:8   => (x-2)^2=9   => (x-2)^2=3^2   => $ left[ begin{matrix} x-2=3   x-2=-3 end{matrix} right.$   => $ left[ begin{matrix} x=5   x=-1 end{matrix} right.$   Vậy x&isin;{5;-1}   c) 75-5 (x-3)^3=700   => 5 (x-3)^3=75-700   => 5 (x-3)^3=-625   => (x-3)^3= -625:5   => (x-3)^3=-125   => (x-3)^3=-5^3   => x-3=-5   => x=-5+3   => x=-2   Vậy x=-2       _____________________           - Mũ chẵn 2 trường hợp.           - Mũ lẻ 1 trường hợp.

landinhngoc97 · Answer

a) 1^2021 + 99 (5 - x) = 94 - (-321) + 279 &rArr;  1 + 99(5 - x)             = 694 &rArr;        99(5 - x)             = 694 - 1  &rArr;        99(5 - x)             = 693 &rArr;             5 - x              = 693 : 99 &rArr;             5 - x              = 7  &rArr;                  x               = 5 - 7 &rArr;                  x               = -2  Vậy x = -2        b) 72 : (x - 2)^2 = 8 &rArr;        (x - 2)^2 = 72 : 8  &rArr;        (x - 2)^2 = 9 &hArr; ( left[  begin{array}{l}x -2=3  x-2=-3 end{array}  right. )  &hArr; ( left[  begin{array}{l}x=5  x=-1 end{array}  right. )   Vậy x &isin; { 5; -1 }       c) 75 - 5(x - 3)^3 = 700 &rArr;     5 (x - 3)^3 = 75 - 700 &rArr;     5 (x - 3)^3 = -625 &rArr;        (x - 3)^3 = -625 : 5  &rArr;        (x - 3)^3 = -125 &rArr;        (x - 3)^3 = (-5)^3 &rArr;           x - 3       = -5 &rArr;          x             = -5 + 3  &rArr;          x             = -2   Vậy x = -2