Bạn tham khảo nhé
Giải thích các bước giải:
Bài 1 :
`a) 3x(x - 2) = 3x^2 - 6x`
`b) (x^2 + 14x + 49):(x + 7) = (x + 7)^2 : (x + 7) = x + 7 \text{ vì } (x + 7)^2 = x^2 + 2.x.7 + 7^2 = x^2 + 14x + 49 \text{ dùng hằng đẳng thức thứ nhất}`
`c) (5x + 2)/(2x + 1) - x/(2x + 1) = (5x + 2 -x)/(2x + 1) = (4x + 2)/(2x + 1) = [2(2x + 1)]/(2x + 1) = 2`
Bài 2 :
`1.a) 3x - 3y = 3(x - y)`
`1.b) x^2 + 4(x + 5) - 25 = x^2 + 4x + 20 - 25 = x^2 + 4x - 5 = x^2 - x + 5x - 5 = x(x - 1) + 5(x - 1) = (x - 1)(x + 5)`
`2) 3x^2 + 12x = 0 => 3x(x + 4) = 0 =>` $\left \{ {{3x = 0} \atop {x + 4 = 0}} \right.$ `=>` $\left \{ {{x=0} \atop {x=-4}} \right.$
`3) (x/(x^2 - 36) - (x - 6)/(x^2 + 6x)) : (x^2 + 6x)/(2x - 6)`
`= (x/[(x + 6)(x - 6)] - (x - 6)/[x(x + 6)] ) : (x(x + 6))/[2(x - 3)]`
`MTC = x(x + 6)(x - 6)`
`= ((x.x)/[x(x + 6)(x - 6)] - [(x - 6)(x - 6)]/[x(x + 6)(x - 6)]) . [2(x - 3)]/[x(x + 6)]`
`=[x^2 - (x^2 - 6x - 6x + 36)]/[x(x + 6)(x - 6)] . [2(x - 3)]/[x(x + 6)] `
`= (x^2 - x^2 + 6x + 6x - 36)/[x(x + 6)(x - 6)]. [2(x - 3)]/[x(x + 6)] = (12x - 36)/[x(x + 6)(x - 6)` . `[2(x - 3)]/[x(x + 6)]`
`= (12(x - 3))/[x(x + 6)(x - 6)] . [2(x - 3)]/[x(x + 6)] = [24(x - 3)^2]/[x(x + 6)^2(x - 6)]`
