Question

help me cíu!!=((

Answer 1

`(x-2)^2/12-(x+1)^2/21=[(x-4)(x-6)]/28`

`<=> [7(x^2-4x+4)]/84-[4(x^2+2x+1)]/84=[3(x^2-6x-4x+24)]/84`

`=>7x^2 -28x+28 - 4x^2 -8x-4 = 3x^2- 18x -12x +72`

`<=> 7x^2 -28x -4x^2 -8x +18x +12x -3x^2 =72-28+4`

`<=>-6x = 48

`<=> x = -8`

Vậy `S={-8}`

Answer 2

 \(\dfrac{\left(X-2\right)^2}{12}\)- \(\dfrac{\left(X+1\right)^2}{21}\)=\(\dfrac{\left(X-4\right)\left(X+6\right)}{28}\)

<=> \(\dfrac{7\left(X-2\right)^2}{84}\)-\(\dfrac{4\left(X+1\right)^2}{84}\)=\(\dfrac{3\left(X-4\right)\left(X-6\right)}{84}\)

<=>7(x-2)² - 4(x+1)² = 3(x-4)(x-6)

<=>7(x² - 4x + 4) - 4(x² + 2x + 1) = 3(x² - 10x + 24)

<=>7x² - 28x + 28 - 4x² - 8x - 4 = 3x² -30x +72

<=>7x² - 4x² - 3x² - 28x - 8x + 30x = - 28 + 4 + 72

<=> 50x = 48

<=> x = \(\dfrac{48}{50}\)

<=> x = \(\dfrac{24}{25}\)

S = \(\left\{\dfrac{24}{25}\right\}\)