tìm x :> x(3x-4)+15x-20=0 helppppppppp

2 bình luận về “tìm x :> x(3x-4)+15x-20=0 helppppppppp”

1. x(3x-4)+15x-20=0

   <=> x.3x+x.(-4)+15x-20=0

   <=> 3x^2-4x+15x-20=0

   <=> 3x^2+11x-20=0

   <=> 3x^2+15x-4x-20=0

   <=> 3x(x+5)-4(x+5)=0

   <=> (3x-4)(x+5)=0

   <=>[(3x-4=0),(x+5=0):}

   <=> [(x=4/3),(x=-5):}

   Vậy x∈{4/3; -5}

   Trả lời
2. x(3x-4)+15x-20=0

   <=>3x^2-4x+15x-20=0

   <=>3x^2+11x-20=0

   <=>3x^2-4x+15x-20=0

   <=>x(3x-4)+5(3x-4)=0

   <=>(3x-4)(x+5)=0

   <=>\(\left[ \begin{array}{l}3x-4=0\\x+5=0\end{array} \right.\) 

   <=>\(\left[ \begin{array}{l}x=\dfrac{4}{3}\\x=-5\end{array} \right.\) 

   Vậy S ={4/3;-5}

   Trả lời