Toán Lớp 7: (x-4).(x+5)=0 60%.x+2/3.x=684 (2x+1/2).(4/5-x)=0

Question

Toán Lớp 7:  (x-4).(x+5)=0 60%.x+2/3.x=684 (2x+1/2).(4/5-x)=0

truonganhthi · Answer

Giải đáp:       Lời giải và giải thích chi tiết:   ( x - 4 ) . ( x + 5 ) = 0   &rarr; x - 4 = 0 hoặc x + 5 = 0   &rarr; x = 0 + 4 hoặc x = 0 - 5   &rarr; x = 4 hoặc x = -5              Vậy x &isin; { 4; -5 }   _________________________   60% . x + 2/3 . x = 684   x . ( 60% + 2/3 ) = 684   x . 19/15 = 684   x = 684 : 19/15   x = 540   __________________________   ( 2x + 1/2 ) . ( 4/5 - x ) = 0   &rarr; 2x + 1/2 = 0 hoặc 4/5 - x = 0   &rarr; 2x = -1/2 hoặc x = 4/5   &rarr; x = -1/2 : 2 hoặc x = 4/5   &rarr; x = -1/4 hoặc x = 4/5            Vậy x &isin; { -1/4; 4/5 }

tonhu12 · Answer

$a)(x-4)(x+5)=0$     &rArr; ( left[  begin{array}{l}x-4=0  x+5=0 end{array}  right. )      &rArr; ( left[  begin{array}{l}x=4  x=-5 end{array}  right. )      $b)60%x+$2/3$.x=684$     $&rArr;$3/5$x+$2/3$x=684$     $&rArr;x$(3/5+2/3)$=684$     $&rArr;$19/15$x=684$     $&rArr;x=540$     $c)(2x+1/2)(4/5-x)=0$     $&rArr;$ ( left[  begin{array}{l}2x+ frac{1}{2}=0   frac{4}{5}-x=0 end{array}  right. )     $&rArr;$ ( left[  begin{array}{l}2x=- frac{1}{2}  x= frac{4}{5} end{array}  right. )     $&rArr;$ ( left[  begin{array}{l}x=- frac{1}{4}  x= frac{4}{5} end{array}  right. )