Tìm x, biết: `a) (3x – 5)(7 – 5x) – (5x + 2) (2 – 3x) = 4 ` `b) 6x^2 – (2x + 5) (3x – 2) = 7.` chúc mừng ngày quốc khánh 2/9/2020

0 bình luận về “Tìm x, biết: `a) (3x – 5)(7 – 5x) – (5x + 2) (2 – 3x) = 4 ` `b) 6x^2 – (2x + 5) (3x – 2) = 7.` chúc mừng ngày quốc khánh 2/9/2020”

1. Đáp án:

   $a) (3x-5)(7-5x)-(5x+2)(2-3x)=4$

   $⇔ 21x-15x²-35+25x-(10x-15x²+4-6x)-4=0$

   $⇔ 21x-15x²-35+25x-10x+15x²-4+6x-4=0$

   $⇔ (-15x²+15x²)+(21x+25x-10x+6x)+(-35-4-4)=0$

   $⇔ 42x-43=0$

   $⇔ x=43/42$

   Vậy $S=${$43/42$}

   $b) 6x²-(2x+5)(3x-2)=7$

   $⇔ 6x²-(6x²-4x+15x-10)-7=0$

   $⇔ 6x²-6x²+4x-15x+10-7=0$

   $⇔ -11x+3=0$

   $⇔ x = 3/11$

   Vậy $S=${$3/11$}

   BẠN THAM KHẢO NHA!!!

    

   Bình luận

2. `a) (3x – 5)(7 – 5x) – (5x + 2) (2 – 3x) = 4`

   `=>21x – 15x^2 – 35 + 25x – (10x – 15x^2 + 4 – 6x) – 4 =0`

   `=>21x – 15x^2 – 35 + 25x – 10x + 15x^2 – 4 + 6x – 4= 0 `

   `=>21x + 25x -10x + 6x = 4 +35+4 `

   `=>32x = 43`

   `=>x=43/42`

   `b) 6x^2 – (2x + 5) (3x – 2) = 7 `

   `=> 6x^2 – (6x^2 – 4x + 15x – 10) = 7 `

   `=> 6x^2 – 6x^2 + 4x – 15x + 10 = 7 `

   `=> 4x – 15x = 7 – 10 `

   `=> -11x = -3 `

   `=> x= 3/11`

   Bình luận