: Giải phương trình . a) x4 – 5×2 + 4 = 0 b) 2×4 –3×2 –2 = 0 c) 2×4-7×2+4=0 d) (x2-9)(x2+7x+6)=0 e) 5×4+2×2–16=10–x2 f) √x-5 =x-7

0 bình luận về “: Giải phương trình . a) x4 – 5×2 + 4 = 0 b) 2×4 –3×2 –2 = 0 c) 2×4-7×2+4=0 d) (x2-9)(x2+7x+6)=0 e) 5×4+2×2–16=10–x2 f) √x-5 =x-7”

1. `a, x^4–5x^2+4=0`
   `<=>x^4-x^2-4x^2+4=0`
   `<=>x^2(x^2-1)-4(x^2-1)=0`
   `<=>(x^2-4)(x^2-1)=0`
   `<=>(x+2)(x-2)(x-1)(x+1)=0`
   `<=>` $\left\{ \matrix{ x+2=0 \hfill \cr  x-2=0 \hfill \cr  x – 1=0 \hfill \\x+1=0} \right. \Leftrightarrow \left\{ \matrix{x=-2 \hfill \cr  x=2 \hfill \cr  x=1 \hfill\\x=-1} \right.$

   `b, 2x^4–3x^2–2=0`
   `<=>2x^4+x^2-4x^2-2=0` 
   `<=>x^2(2x^2+1)-2(2x^2+1)`
   `<=>(x^2-2)(2x^2+1)=0`
   `<=>(x-sqrt2)(x+sqrt2)(`
   `<=>` $\left\{ \matrix{ x-\sqrt2=0 \hfill\\x+\sqrt2=0\hfill\\2x^2+1=0(vô\ lí)   } \right. \Leftrightarrow \left\{ \matrix{x=\sqrt2 \hfill\\x=-\sqrt2  } \right.$

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