Giúp mình với ạ , mình cảm ơn

`b)`

`(-3x+2)(4x-5)`

`=(-3x.4x) + (-3x.-5)+(2.4x)+(2.-5)`

`=-12x^2 +15x+8x-10`

`=-12x^2 +23x-10`

`c)`

`(x-2)(x^2 +3x-1)`

`=(x.x^2) + (x.3x) + (x.-1) + (-2.x^2) + (-2.3x) + (-2.-1)`

`=x^3 +3x^2 -x -2x^2 -6x+2`

`=x^3 + x^2 -7x+2`

`d)`

`3x(2x+5)-6x(x-4)=117`

`<=>6x^2 +15x -6x^2 +24x =117`

`<=> 39x = 117`

`<=> x = 3`

Vậy `x=3`.

`e)`

`-2x(10x-5)+4x(5x+1)=-70`

`<=>-20x^2 +10x +20x^2 +4x=-70`

`<=>14x=-70`

`<=>x=-5`

Vậy `x=-5`.

`f)`

`-7x(6x+3)+2x(21x-5)=-186`

`<=>-42x^2 -21x + 42x^2 - 10x = -186`

`<=> -31x = -186`

`<=>x = 6`

Vậy `x=6`.