Đáp án:
Giải thích các bước giải:
Bài 4:
$1) 0,6x(x - 0,5) - 0,3x(2x - 1,3) = -0,138$
$=> 0,6x^2 - 0,3x - 0,6x^2 + 0,39x = - 0,138$
$=> (0,6x^2 - 0,6x^2) + (-0,3x + 0,39x) = -0,138$
$=> 0,09x = -0,138$
$=> x = \frac{-23}{15}$
$ Vậy x = \frac{-23}{15}$
$2) 6x^2 - (2x + 5)(3x - 2) = 7$
$=> 6x^2 - (6x^2 - 4x + 15x - 10) = 7$
$=> (6x^2 - 6x^2) + (4x - 15x) + 10 = 7$
$=> -11x + 10 = 7$
$=> -11x = -3$
$=> x = \frac{3}{11}$
$Vậy x = \frac{3}{11}$
$3) (2x - 3)(2x + 1) + 35 = 4x(x - 5)$
$=>(4x^2 + 2x - 6x - 3) + 35 = 4x^2 - 20x$
$=>(4x^2 + 2x - 6x - 3) + 35 - 4x^2 + 20x = 0$
$=>(4x^2 - 4x^2) + (2x - 6x + 20x) + (-3 + 35) = 0$
$=> 16x + 32 = 0$
$=> 16x = -32$
$=> x = -2$
$Vậy x = -2$
$4) 6x(5x + 3) + 3x(1 - 10x) = 7$
$=> 30x^2 + 18x + 3x - 30x^2 = 7$
$=> (30x^2 - 30x^2) + (18x + 3x) = 7$
$=> 21x = 7$
$=> x = \frac{1}{3}$
$Vậy x = \frac{1}{3}$
$5) (3x - 3)(5 - 21x) + (7x + 4)(9x - 5) = 44$
$=>(15x - 63x^2 - 15 + 63x) + (63x^2 - 35x + 36x - 20) = 44$
$=>(-63x^2 + 63x^2) + (15x + 63x - 35x + 36x) + (-15 - 20) = 44$
$=> 79x - 35 = 44$
$=> 79x = 79$
$=> x = 1$
$Vậy x = 1$
$6) (x + 1)(x + 2)(x + 5) - x^2(x + 8) = 27$
$=>(x^2 + 2x + x + 2)(x +5) - (x^3 + 8x^2) = 27$
$=>(x^2 + 3x + 2)(x + 5) - (x^3 + 8x^2) = 27$
$=>(x^3 + 5x^2 + 3x^2 + 15x + 2x + 10) - (x^3 + 8x^2) = 27$
$=>(x^3 + 8x^2 + 17x + 10) - (x^3 + 8x^2) = 27$
$=>(x^3 - x^3) + (8x^2 - 8x^2) + 17x + 10 = 27$
$=> 17x + 10 = 27$
$=> 17x = 17$
$=> x = 1$
$Vậy x = 1$
$7) (2x + 3)(x - 4) + (x - 5)(x - 2) = (3x - 5)(x - 4)$
$=>(2x^2 - 8x + 3x - 12) + (x^2 - 2x - 5x + 10) = 3x^2 - 12x - 5x + 20$
$=> (2x^2 - 8x + 3x - 12) + (x^2 - 2x - 5x + 10) - 3x^2 + 12x + 5x = 20$
$=> (2x^2 + x^2 - 3x^2) + (-8x + 3x - 2x - 5x + 12x + 5x) + (-12 + 10) = 20$
$=> 5x - 2 = 20$
$=> 5x = 22$
$=> x = \frac{22}{5}$
$ Vậy x = \frac{22}{5}$
$8) 8(x - 3)(3x + 2) - (14x + 7)(x + 4) = (2x + 1)(5x - 1)$
$=>8(3x^2 + 2x - 9x - 6) - (14x^2 + 56x + 7x + 28) = 10x^2 - 2x + 5x - 1$
$=> (24x^2 + 16x - 72x - 48) - (14x^2 + 63x + 28) - 10x^2 + 2x - 5x + 1 = 0$
$=> (24x^2 - 14x^2 - 10x^2) + (16x - 72x - 63x + 2x - 5x) + (-48 - 28 + 1) = 0$
$=> -122x - 75 = 0$
$=> -122x = 75$
$=> x = \frac{-75}{122}$
$ Vậy x = \frac{-75}{122}$
