Toán Lớp 8: Tìm x biết: a) 9x^2-6x+1=0 b) 15x-3-6x (5x-1)=0

Question

Toán Lớp 8:  Tìm x biết: a) 9x^2-6x+1=0 b) 15x-3-6x (5x-1)=0

lanhuongthu · Answer

~ Bạn tham khảo ~ a, 9x^2 - 6x + 1 = 0 <=> (3x + 1)^2 = 0 <=> 3x+1=0 <=> 3x=-1 <=> x=-1/3 Vậy S={-1/3} b, 15x-3-6x(5x-1)=0 <=> 3(5x-1) - 6x(5x-1) =0 <=> (5x-1)(3-6x) =0 <=> 3(1-2x)(5x-1)=0 (⇔ left[ begin{array}{l}1-2x=0 5x-1=0 end{array} right. ) (⇔ left[ begin{array}{l}x= dfrac12 x= dfrac15 end{array} right. ) Vậy S={1/2;1/5}

bichhhathu · Answer

a) 9x^2-6x+1=0         &hArr; (3x)^2-2.3.1.x+1=0         &hArr;(3x-1)^2=0         &hArr;3x-1=0         &hArr;3x=1         &hArr;x=1/3         S= {1/3}          b) 15x-3-6x (5x-1)=0          &hArr;15x-3-30x^2+6x=0         &hArr;30x^2-21x+3=0 (chuyển hết sang vế phải )          &hArr;2x(5x-1)-(5x-1)=0         &hArr;(2x-1)(5x-1)=0         &hArr;$ left[ begin{matrix} 2x-1=0   5x-1=0 end{matrix} right.$         &hArr;$ left[ begin{matrix} x=1/2   x=1/5 end{matrix} right.$         S={1/2;1/5}         xin hay nhất !!!!!         #aw