Tìm x,biết :a)5(x-3)(x-7)-(5x+1)(x-2)=25 b)3(x-7)(x-5)-(x-1)(3x+2)=-13 14/08/2021 Bởi Piper Tìm x,biết :a)5(x-3)(x-7)-(5x+1)(x-2)=25 b)3(x-7)(x-5)-(x-1)(3x+2)=-13
Đáp án: \(a,\ x=2\\ b,\ x=\dfrac{24}{7}\) Giải thích các bước giải: \(a,\ 5(x-3)(x-7)-(5x+1)(x-2)=25\\ ⇔5(x^2-10x+21)-5x^2+9x+2=25\\ ⇔5x^2-50x+105-5x^2+9x+2=25\\ ⇔(5x^2-5x^2)+(-50x+9x)=25-2-105\\ ⇔-41x=-82\\ ⇔x=\dfrac{-82}{-41}=2\\ \text{Vậy x = 2}\\ 3(x-7)(x-5)-(x-1)(3x+2)=-13\\ ⇔3(x^2-12x+35)-3x^2+x+2=-13\\ ⇔3x^2-36x+105-3x^2+x+2=-13\\ ⇔(3x^2-3x^2)+(-36x+x)=-13-2-105\\ ⇔-35x=-120\\ ⇔x=\dfrac{-120}{-35}=\dfrac{24}{7}\\ \text{Vậy x = $\dfrac{24}{7}$}\) chúc em học tốt! Bình luận
`a) 5(x-3)(x-7)-(5x+1)(x-2)=25` `5(x^2 -3x-7x+21)-(5x^2 +x-10x-2)=25` `5x^2 -15x-35x+105-5x^2 -x+10x+2=25` `-41x+107=25` `-41x=-82` `x=2` `b) 3(x-7)(x-5)-(x-1)(3x+2)=-13` `3(x^2 -7x-5x+35)-(3x^2 -3x+2x-2)=-13` `3x^2 -21x-15x +105-3x^2 +3x-2x+2=-13` `-35x+107=-13` `-35x=-120` `x=24/7` chúc học tốt Bình luận
Đáp án:
\(a,\ x=2\\ b,\ x=\dfrac{24}{7}\)
Giải thích các bước giải:
\(a,\ 5(x-3)(x-7)-(5x+1)(x-2)=25\\ ⇔5(x^2-10x+21)-5x^2+9x+2=25\\ ⇔5x^2-50x+105-5x^2+9x+2=25\\ ⇔(5x^2-5x^2)+(-50x+9x)=25-2-105\\ ⇔-41x=-82\\ ⇔x=\dfrac{-82}{-41}=2\\ \text{Vậy x = 2}\\ 3(x-7)(x-5)-(x-1)(3x+2)=-13\\ ⇔3(x^2-12x+35)-3x^2+x+2=-13\\ ⇔3x^2-36x+105-3x^2+x+2=-13\\ ⇔(3x^2-3x^2)+(-36x+x)=-13-2-105\\ ⇔-35x=-120\\ ⇔x=\dfrac{-120}{-35}=\dfrac{24}{7}\\ \text{Vậy x = $\dfrac{24}{7}$}\)
chúc em học tốt!
`a) 5(x-3)(x-7)-(5x+1)(x-2)=25`
`5(x^2 -3x-7x+21)-(5x^2 +x-10x-2)=25`
`5x^2 -15x-35x+105-5x^2 -x+10x+2=25`
`-41x+107=25`
`-41x=-82`
`x=2`
`b) 3(x-7)(x-5)-(x-1)(3x+2)=-13`
`3(x^2 -7x-5x+35)-(3x^2 -3x+2x-2)=-13`
`3x^2 -21x-15x +105-3x^2 +3x-2x+2=-13`
`-35x+107=-13`
`-35x=-120`
`x=24/7`
chúc học tốt