giúp mk với ạ 5x mũ 2+16x +3=0 (4x +14) mũ 2=(7x +21) mũ 2

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1. Đáp án:

    

   Giải thích các bước giải:

    a,5x²+16x+3=0

   <=> 5x²+15x+x+3=0

   <=> (5x²+15x)+(x+3)=0

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

   <=> (x+3)(5x+1)=0

   <=> $\left \{ {{x+3=0} \atop {5x+1=0}} \right.$

   <=> $\left \{ {{x=-3} \atop {x=\frac{1}{5}}} \right.$

   Vậy  $\left \{ {{x=-3} \atop {x=\frac{1}{5}}} \right.$

   b,(4x +14) ²=(7x +21)²

   <=> 16x²+112x+196=49x²+294x+441

   <=> 16²-49x²+112x-294x-441+196=0

   <=>-33x²-182x-254=0

   sai đề ạ 

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2. 1,

   $5x^2+16x+3=0$
   $5x^2+15x+x+3=0$
   $↔5x(x+3)+(x+3)=0$
   $↔(x+3)(5x+1)=0$
   $↔\left[\begin{array}{l}x+3=0\\5x+1=0\end{array}\right.↔\left[\begin{array}{l}x=-3\\x=-\dfrac15\end{array}\right.$
   Vậy `x \in {-3;-1/5}`

   2,

   $(4x+14)^2=(7x+21)^2$
   $↔\left[\begin{array}{l}4x+14=7x+21\\4x+14=-7x-21\end{array}\right.↔\left[\begin{array}{l}3x=-7\\11x=-35\end{array}\right.↔\left[\begin{array}{l}x=-\dfrac73\\x=-\dfrac{35}{11}\end{array}\right.$

   Vậy `x\in {-7/3;-35/11}`

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