Toán Lớp 8: a) (x-1)^2=x-1 b) (2x-1)^2-25=0 c) 8x^3-50x=0 d) 3x(x-1)+x-1=0 e) 2(x+3)-x^2-3x=0 f) 4x^2-25-(2x-5).(2x+7)=0

Question

Toán Lớp 8:  a) (x-1)^2=x-1 b) (2x-1)^2-25=0 c) 8x^3-50x=0 d) 3x(x-1)+x-1=0 e) 2(x+3)-x^2-3x=0 f) 4x^2-25-(2x-5).(2x+7)=0

diemmyhoa · Answer

Đáp án:       Giải thích các bước giải:

dinhcongson · Answer

$ displaystyle  begin{array}{{>{ displaystyle}l}} ( x-1)^{2} =x-1     chia  hai  vế  cho  x-1  ta  c&oacute;     x-1=1      rightarrow x=2     Vậy....     b)   ( 2x-1)^{2} -25=0      rightarrow ( 2x-1+5)( 2x-1-5) =0     ( 2x+4)( 2x-6) =0      left[  begin{array}{l l} 2x+4=0 &    2x-6=0 &  end{array}  right. rightarrow  left[  begin{array}{l l} x=-2 &    x=3 &  end{array}  right.      c) 8x^{3} -50x=0    rightarrow 2x left( 4x^{2} -25 right) =0    rightarrow 2x( 2x-5)( 2x+5) =0      rightarrow  left[  begin{array}{l l} x=0 &    2x-5=0 &    2x+5=0 &  end{array}  right. rightarrow  left[  begin{array}{l l} x=0 &    x= frac{5}{2} &    x= frac{-5}{2} &  end{array}  right.      d) 3x( x-1) +x-1=0     ( x-1)( 3x+1) =0      rightarrow  left[  begin{array}{l l} x-1=0 &    3x+1=0 &  end{array}  right. rightarrow  left[  begin{array}{l l} x=1 &    x= frac{-1}{3} &    end{array}  right.   e) 2( x+3) -x^{2} -3x=0     2( x+3) -x( x+3) =0     ( x+3)( 2-x) =0      left[  begin{array}{l l} x+3=0 &    2-x=0 &  end{array}  right. rightarrow  left[  begin{array}{l l} x=-3 &    x=2 &  end{array}  right.      f) 4x^{2} -25-( 2x-5)( 2x+7) =0     ( 2x-5)( 2x+5) -( 2x-5)( 2x+7) =0     ( 2x-5)( 2x+5-2x-7) =0     -2( 2x-5) =0      rightarrow 2x-5=0      rightarrow x= frac{5}{2}    end{array}$