Toán Lớp 8: tìm x a2x^2-10x=0 b4x^2-24x+36=(x-3)^2 c(8x^3-7Xx^2):x^2=3x căn bậc 9/25 lưu ý đề bài câu c-x^2 hay :x^2 ý

Question

Toán Lớp 8:  tìm x  a2x^2-10x=0 b4x^2-24x+36=(x-3)^2 c(8x^3-7Xx^2):x^2=3x căn bậc 9/25 lưu ý  đề bài câu c-x^2 hay :x^2 ý

thanhbinh2k5 · Answer

Giải đáp: + Lời giải và giải thích chi tiết:    a) 2x^2 -10x =0   &hArr;2x(x-5)=0   &hArr; ( left[  begin{array}{l}2x=0  x-5=0 end{array}  right. )    &hArr; ( left[  begin{array}{l}x=0  x=5 end{array}  right. )    Vậy x=0 hoặc x=5   b)4x^2 -24x+36 =(x-3)^2   &hArr;[(2x)^2 -2.2x.6 +6^2]-(x-3)^2=0   &hArr;(2x-6)^2 -(x-3)^2 =0   &hArr;(2x-6-x+3)(2x-6+x-3)=0   &hArr;(x-3)(3x-9)=0   &hArr; ( left[  begin{array}{l}x-3=0  3x-9=0 end{array}  right. )    &hArr; ( left[  begin{array}{l}x=3  x=3 end{array}  right. )    Vậy x=3   c) (8x^3 -7x^2):x^2 =3x sqrt{9/25}   &hArr;8x^3 :x^2 -7x^2 :x^2 =3x. 3/5   &hArr;8x -7=9/5 x   &hArr;8x-9/5 x =7   &hArr;31/5 x=7   &hArr;x=7 : 31/5   &hArr;x=35/31   Vậy x=35/31

cobexinhdep · Answer

#laviken#   a)2x^2-10x=0   =>2x(x-5)=0   =>$ left[ begin{matrix} 2x=0   x-5=0 end{matrix} right.$    =>$ left[ begin{matrix} x=0   x=5 end{matrix} right.$   Vậy x={0; 5}   b)4x^2-24x+36=(x-3)^2   =>4x^2-24x+36=x^2-6x+9   =>4x^2-14x+36-x^2-6x+9=0   =>3x^2-18x+27=0   =>3(x^2-6x+9)=0   =>3(x-3)^2=0   =>(x-3)^2=0   =>x-3=0   =>x=3   Vậy x=3   c)(8x^3-7x^2):x^2=3x+ sqrt{9/25}   =>8x-7=3x+3/5   =>8x-3x=3/5+7   =>5x=38/5   =>x=38/5:5   =>x=38/25   Vậy x=38/25