tìm x biết 1.(x-3)^3 -(x-3)(x^2+3x+9)+9(x+1)^2=15 2.x(x-5)(x+5)-(x+2)(x^2-2x+4)=3 3.(x+4)(x^2-4x+16)-x(x-5)(x+5)=264

0 bình luận về “tìm x biết 1.(x-3)^3 -(x-3)(x^2+3x+9)+9(x+1)^2=15 2.x(x-5)(x+5)-(x+2)(x^2-2x+4)=3 3.(x+4)(x^2-4x+16)-x(x-5)(x+5)=264”

1. `a,(x-3)^3-(x-3)(x^2+3x+9)+9(x+1)^2=15`

   `⇔x^3-9x^2+27x-27-x^3+27+9(x^2+2x+1)=15`

   `⇔x^3-9x^2+27x-27-x^3+27+9x^2+18x+9=15`

   `⇔45x=6`

   `⇔x=2/15`

   `b, x(x-5)(x+5)-(x+2)(x^2-2x+4)=3`

   `⇔x(x^2-25)-x^3-8=3`

   `⇔x^3-25x-x^3-8=3`

   `⇔-25x=11`

   `⇔x=-11/25`

   `c,(x+4)(x^2-4x+16)-x(x-5)(x+5)=264`

   `⇔x^3+64-x(x^2-25)=264`

   `⇔x^3+64-x^3+25x=264`

   `⇔25x=200`

   `⇔x=8`

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2. Đáp án:

   $1. ( x – 3)³ – ( x -3)(x² + 3x + 9)  + 9( x + 1)² = 15$

   $<=> x³ – 9x² + 27x – 27 – (x³ – 27 )+ 9(x² + 2x + 1) = 15$

   $<=> x³ – 9x² + 27x – 27 – x³ + 27 + 9x² + 18x + 9 = 15$

   $<=> 45x + 9 = 15$

   $<=> 45x = 6$

   $<=> x = 2/15$

   Vậy$ x = 2/15$

   $2. x(x – 5)(x + 5)- (x +2)(x² -2x +4) = 3$

   $<=> x(x² – 25) – ( x³ + 8) = 3$

   $<=> x³ – 25x – x³ – 8 = 3$

   $<=> – 25x = 11$

   $<=> x = -11/25$

   Vậy $x = – 11/25$

   $3. (x + 4)( x² – 4x + 16) – x(x – 5)(x +5)  = 264$

   $<=> x³ + 64 – x( x²  – 25) = 264$

   $<=> x³ + 64 – x³ + 25x = 264$

   $<=> 25x = 200$

   $<=>   x = 8$

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