Toán Lớp 8: GIÚP VỚI!!!!! a)25x^2-2=0 b)x^2-25=6x-9 c)(2x-10)^2-(2x+5)(2x-5)=18 d)5x(x-3)-2x+6=0 PLEASE!!!

Question

Toán Lớp 8:  GIÚP VỚI!!!!! a)25x^2-2=0 b)x^2-25=6x-9 c)(2x-10)^2-(2x+5)(2x-5)=18 d)5x(x-3)-2x+6=0 PLEASE!!!

hauthanhyen98 · Answer

a)  25x&sup2; - 2 = 0   &hArr; 25x&sup2; = 2   &hArr; x&sup2; = $ frac{2}{25}$    &hArr; x = &plusmn; $ sqrt[]{ frac{2}{25}}$ = &plusmn; $ frac{&radic;2}{5}$    b) x&sup2; - 25 = 6x - 9   &hArr; x&sup2; -25 + 9 - 6x = 0   &hArr; x&sup2; - 6x - 16 = 0   &hArr; ( x&sup2; - 6x + 9 ) -25 = 0   &hArr; ( x-3)&sup2; - 5&sup2; = 0   &hArr; ( x-3-5)(x-3+5) = 0   &hArr;  ( left[  begin{array}{l}x=-8  x=-2 end{array}  right. )    c) ( 2x - 10)&sup2; - ( 2x - 5)(2x+5) = 18   &hArr; ( 2x-10)&sup2; - ( 4x&sup2; - 25) = 18   &hArr; 4x&sup2; - 40x + 100 - ( 4x&sup2; - 25 ) = 18   &hArr; -40x = 18 - 100 -25   &hArr; -40x = -107   &hArr; x = 2, 675   d) 5x( x-3) - 2x + 6 = 0   &hArr; 5x(x-3) -2( x-3) = 0   &hArr; ( x-3)(5x-2) = 0   &hArr;  ( left[  begin{array}{l}x=3  x= frac{2}{5}  end{array}  right. )

minhtuquynh · Answer

Giải đáp + Lời giải và giải thích chi tiết:    a)25x&sup2;-2=0     25x&sup2; = 2     x&sup2; =  frac{2}{25}     x = &plusmn;  frac{ sqrt{2}}{5}     b) x&sup2; - 25 = 6x - 9     x&sup2; - 6x - 25 + 9 = 0     x&sup2; - 6x - 16 = 0     x&sup2; - 8x + 2x - 16 = 0     x(x-8) + 2(x-8) = 0     (x-8)(x+2) = 0      ( left[  begin{array}{l}x=8  x=-2 end{array}  right. )      c)     (2x - 10)&sup2; - (2x + 5)(2x-5) = 18     4x&sup2; - 40x + 100 - (4x&sup2; - 25) = 18     4x&sup2; - 40x + 100 - 4x&sup2; + 25 = 18     -40x + 125 = 18     40x = 107     x =  frac{107}{40}     d)     5x(x-3) - 2x + 6 = 0     5x&sup2; - 15x - 2x + 6 = 0     5x&sup2; - 17x + 6 = 0     5x&sup2; - 2x - 15x + 6 = 0     x(5x-2) - 3(5x - 2) = 0     (x-3)(5x-2) = 0      ( left[  begin{array}{l}x=3  x= dfrac{2}{5} end{array}  right. )