Toán Lớp 8: 9x^2=1-(3x+1)(2x-9). GIúp mình vss

Question

Toán Lớp 8:  9x^2=1-(3x+1)(2x-9). GIúp mình vss

ngoclanquynh · Answer

$ 9x^2=1-(3x+1)(2x-9) $      $ 9x^2=1-6x^2+25x+9 $      $ 9x^2&minus;1+6x^2&minus;25x&minus;9=0 $     $ 15x^2-25x-10=0 $      $ 15x^2+30x&minus;5x&minus;10=0 $     $ 15x.(x+2)&minus;5.(x+2)=0 $      $ (15x&minus;5).(x+2)=0 $     $ &rArr; $  ( left[  begin{array}{l}15x-5=0  x+2=0 end{array}  right. )      $ &rArr; $  ( left[  begin{array}{l}x=(0+5):15=5:15=1/3  x=0-2=-2 end{array}  right. )

haiyemy · Answer

$ text{ @HV }$   ${ 9x^2 = 1 - (3x + 1).(2x - 9) }$   ${ &hArr; 9x^2 = 1 - 6x^2 + 25x + 9 }$   ${ &hArr; 9x^2 - 1 + 6x^2 - 25x - 9 = 0 }$   ${ &hArr; 15x^2 - 25x - 10 = 0 }$   ${ &hArr; 15x^2 + 30x - 5x - 10 = 0 }$   ${ &hArr; 15x.(x + 2) - 5.(x + 2) = 0 }$   ${ &hArr; (15x - 5).(x + 2) = 0 }$   ${ &hArr;  left[ begin{matrix} 15x - 5 = 0   x + 2 = 0 end{matrix} right. }$   ${ &hArr;  left[ begin{matrix} x =  dfrac{1}{3}   x = -2 end{matrix} right. }$   Vậy phương tr&igrave;nh c&oacute; tập nghiệm $ text{ S = {$ dfrac{1}{3}$ ; -2} }$