Toán Lớp 8: tìm x (2x-3)²-4x(x-7)=9 (2x-3)²-9x²=0

Question

Toán Lớp 8:  tìm x (2x-3)²-4x(x-7)=9 (2x-3)²-9x²=0

ngocle44 · Answer

Giải đáp+Lời giải và giải thích chi tiết: (2x-3)^2-4x(x-7)=0 <=> (2x)^2-2.2x.3+3^2-4x.x+4x.7=9 <=> 4x^2-12x+9-4x^2+28x=9 <=> (4x^2-4x^2)+(28x-12x)+9=9 <=> 16x+9=9 <=> 16x=9-9 <=> 16x=0 <=> x=0 Vậy x=0 - - - - - - - - - - - - - - - - - - - - (2x-3)^2-9x^2=0 <=> (2x)^2-2.2x.3+3^2-9x^2=0 <=> 4x^2-12x+9-9x^2=0 <=> (4x^2-9x^2)-12x+9=0 <=> -5x^2-12x+9=0 <=> -5x^2+3x-15x+9=0 <=> -x(5x-3)-3(5x-3)=0 <=> (-x-3)(5x-3)=0 <=> -(x+3)(5x-3)=0 <=> [(x+3=0),(5x-3=0):} <=> [(x=-3),(5x=3):} <=> [(x=-3),(x=3/5):} Vậy x in {-3;3/5}

kimoanh34 · Answer

( 2x - 3 )^2 - 4x ( x- 7 ) =9     &hArr; 4x^2 - 12x +9 - 4x^2 + 28x =9     &hArr; 16x = 0     &rArr; x = 0    Vậy  x=0    ----------------------    ( 2x - 3 )^2 - 9x^2 =0     &hArr; ( 2x - 3 )^2 - ( 3x )^2 =0     &hArr; ( 2x - 3 - 3x ) ( 2x - 3 + 3x ) =0     &hArr; ( - x - 3 ) ( 5x - 3 ) =0     &hArr;   ( left[  begin{array}{l}- x - 3=0  5x - 3=0 end{array}  right. )     &rArr;   ( left[  begin{array}{l}x=-3  x= dfrac{3}{5} end{array}  right. )    Vậy  x &isin; { -3 ;  frac{3}{5} }