Toán Lớp 6: (x-5).(2x+6)=0 25.(x^2-10)-75=9900

Question

Toán Lớp 6:  (x-5).(2x+6)=0 25.(x^2-10)-75=9900

catlantuong · Answer

$ text{a)}$   $ text{( x - 5 ) . ( 2x + 6 ) = 0}$   $ text{&hArr; $ left[ begin{matrix}x+5=0   2x+6=0 end{matrix} right.$}$   $ text{&hArr; $ left[ begin{matrix}x=0+5   2x=0-6 end{matrix} right.$}$   $ text{&hArr; $ left[ begin{matrix}x=5   2x=-6 end{matrix} right.$}$   $ text{&hArr; $ left[ begin{matrix}x=5  x= ( -6 ) : 2 end{matrix} right.$}$   $ text{&hArr; $ left[ begin{matrix}x=5  x=-3 end{matrix} right.$}$   $ text{Vậy x = $ left[ begin{matrix}5   -3 end{matrix} right.$}$   $ text{b)}$   $ text{25 . ( x&sup2; - 10 ) - 75 = 9900}$   $ text{&hArr; 25 . ( x&sup2; - 10 ) = 9900 + 75}$   $ text{&hArr; 25 . ( x&sup2; - 10 ) = 9975}$   $ text{&hArr; x&sup2; - 10 = 9975 : 25}$   $ text{&hArr; x&sup2; - 10 = 399}$   $ text{&hArr; x&sup2; = 399 + 10}$   $ text{&hArr; x&sup2; = 409}$   $ text{&hArr; x = $ left[ begin{matrix}-&radic;409   &radic;409 end{matrix} right.$}$

hienchaudiem · Answer

(x-5).(2x+6)=0 TH1:x-5=0<=>x=5 TH2:2x+6=0<=>2x=-6<=>x=-3 Vậy x in {5;-3} 25.(x^2-10)-75=9900 <=>25(x^2-10)=9975 <=>x^2-10=399 <=>x^2=409 <=>x=+- sqrt[409] Vậy x= sqrt[409] hoặc x=- sqrt[409]