Toán Tìm x biết: a)x(x-3)+5x=x^2-8 b) 3(x+4)-x^2-4x=0 c) 7x^3+12x-4x=0 06/08/2021 By Aaliyah Tìm x biết: a)x(x-3)+5x=x^2-8 b) 3(x+4)-x^2-4x=0 c) 7x^3+12x-4x=0
`a)x(x-3)+5x=x^2-8` `x(x-3)+5x-x^2+8=0` `x^2-3x+5x-x^2+8=0` `2x+8=0` `2x=-8` `x=-8:2` `x=-4` `b) 3(x+4)-x^2-4x=0` `3(x+4)-(x^2+4x)=0` `3(x+4)-x(x+4)=0` `(x+4)(3-x)=0` `=> x+4=0` hoặc `3-x=0` `=> x=-4` hoặc `x=3` `c) 7x^3+12x^2-4x=0` `x.(7x^3+12x-4x)=0` `x(7x-2)(x+2)=0` `=> x=0` hoặc `7x-2=0` hoặc `x+2=0` `=> x=0` hoặc `x= 2/7` hoặc `x=-2` Trả lời
Đáp án: a)x(x−3)+5x=x2−8 x(x−3)+5x−x2+8=0 x2−3x+5x−x2+8=0 2x+8=0 2x=−8 x=−8:2 x=−4 b)3(x+4)−x2−4x=0 3(x+4)−(x2+4x)=0 3(x+4)−x(x+4)=0 (x+4)(3−x)=0 TH1:x+4=0 ⇒x=−4 TH2: 3−x=0 ⇒x=3 c)7x3+12x2−4x=0 x.(7x3+12x−4x)=0 x(7x−2)(x+2)=0 TH1: x=0 ⇒x=0 TH2:7x-2=0 ⇒x=2/7 TH3:x+2=0 ⇒ x=−2 Trả lời
`a)x(x-3)+5x=x^2-8`
`x(x-3)+5x-x^2+8=0`
`x^2-3x+5x-x^2+8=0`
`2x+8=0`
`2x=-8`
`x=-8:2`
`x=-4`
`b) 3(x+4)-x^2-4x=0`
`3(x+4)-(x^2+4x)=0`
`3(x+4)-x(x+4)=0`
`(x+4)(3-x)=0`
`=> x+4=0` hoặc `3-x=0`
`=> x=-4` hoặc `x=3`
`c) 7x^3+12x^2-4x=0`
`x.(7x^3+12x-4x)=0`
`x(7x-2)(x+2)=0`
`=> x=0` hoặc `7x-2=0` hoặc `x+2=0`
`=> x=0` hoặc `x= 2/7` hoặc `x=-2`
Đáp án:
a)x(x−3)+5x=x2−8
x(x−3)+5x−x2+8=0
x2−3x+5x−x2+8=0
2x+8=0
2x=−8
x=−8:2
x=−4
b)3(x+4)−x2−4x=0
3(x+4)−(x2+4x)=0
3(x+4)−x(x+4)=0
(x+4)(3−x)=0
TH1:x+4=0
⇒x=−4
TH2: 3−x=0
⇒x=3
c)7x3+12x2−4x=0
x.(7x3+12x−4x)=0
x(7x−2)(x+2)=0
TH1: x=0
⇒x=0
TH2:7x-2=0
⇒x=2/7
TH3:x+2=0
⇒ x=−2