Toán Lớp 8: Bài 4.Tìm x biết :
a) (2x+3) (x-4) +(x-5) (x-2) = (3x-5) (x-4)
b) (3x -5 ) ( 7- 5x) – (5x +2) ( 2 -3x) = 4
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Toán Lớp 8: Bài 4.Tìm x biết :
a) (2x+3) (x-4) +(x-5) (x-2) = (3x-5) (x-4)
b) (3x -5 ) ( 7- 5x) – (5x +2) ( 2 -3x) = 4
Comments ( 2 )
$(2x+3)(x-4)+(x-5)(x-2)=(3x-5)(x-4)$
$⇔2x^{2}-8x+3x-12+x^{2}-2x-5x+10=3x^{2}-12x-5x+20$
$⇔2x^{2}-8x+3x-12+x^{2}-2x-5x+10-3x^{2}+12x+5x-20=0$
$⇔5x-22=0$
$⇔5x=22$
$⇔x=\dfrac{22}{5}$
Vậy $x=\dfrac{22}{5}$
$(3x-5)(7-5x)–(5x+2)(2-3x)=4$
$⇔21x-15x^{2}-35+25x-(10x-15x^{2}+4-6x)-4=0$
$⇔21x-15x^{2}-35+25x-10x+15x^{2}-4+6x-4=0$
$⇔42x-43=0$
$⇔42x=43$
$⇔x=\dfrac{43}{42}$
Vậy $x=\dfrac{43}{42}$