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f(x)=ax-b
=> f(2)=2a-b=8(thay x=2)
f(-2)=-2a-b=0(Thay x=-2)
Cộng vế với vế => 2a-b-2a-b=8
=> -2b=8
=>b=-4
=> a=2
![](https://rs.olm.vn/images/avt/0.png?1311)
a, f(0,5)
=>f = 5 x 0,5^2-2
= 5 x 0,25-2
= 1,25 -2
= -0,75
f(-0,2)
=>f = 5 x (-0,2)^2-2
= 5 x 0,04-2
= 0,2-2
= -1,8
....................
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`1,`
`f(x)+g(x)=(5x^4+4x^2-2x+7)+(4x^4-2x^3+3x^2+4x-1)`
`= 5x^4+4x^2-2x+7+4x^4-2x^3+3x^2+4x-1`
`=(5x^4+4x^4)-2x^3+(4x^2+4x^2)+(-2x+4x)+(7-1)`
`= 9x^4-2x^3+8x^2+2x+6`
Đề phải là `f(x)-g(x)` chứ nhỉ :v?
`f(x)-g(x)=(5x^4+4x^2-2x+7)-(4x^4-2x^3+3x^2+4x-1)`
`= 5x^4+4x^2-2x+7-4x^4+2x^3-3x^2-4x+1`
`= (5x^4-4x^4)+2x^3+(-2x-4x)+(4x^2-3x^2)+(7+1)`
`= x^4+2x^3-6x+x^2+8`
![](https://rs.olm.vn/images/avt/0.png?1311)
a) \(f\left(x\right)-g\left(x\right)=\left[x\left(x^2-2x+7\right)-1\right]-\left[x\left(x^2-2x-1\right)-1\right]\)
\(f\left(x\right)-g\left(x\right)=x^3-2x^2+7x-1-x^3+2x^2+x+1\)
\(f\left(x\right)-g\left(x\right)=8x\)
\(f\left(x\right)+g\left(x\right)=x\left(x^2-2x+7\right)-1+x\left(x^2-2x-1\right)-1\)
\(f\left(x\right)+g\left(x\right)=x^3-2x^2+7x-1+x^3-2x^2-x-1\)
\(f\left(x\right)+g\left(x\right)=2x^3-4x^2+6x-2\)
b) 8x=0
=> x=0
=> Nghiệm đa thức f(x)-g(x)
c) Thay \(x=-\frac{3}{2}\)vào BT f(x)+g(x) ta được :
\(2.\left(-\frac{3}{2}\right)^3-4\left(-\frac{3}{2}\right)^2+6\left(-\frac{3}{2}\right)-2\)
\(=6,75+9-9-2\)
\(=4,75\)
#H
![](https://rs.olm.vn/images/avt/0.png?1311)
Ta có
Thay x = 1/2 : \(f\left(\frac{1}{2}\right)+3f\left(2\right)=\frac{1}{4}\)
Thay x = 2: \(f\left(2\right)+3f\left(\frac{1}{2}\right)=4\)
\(\Rightarrow\left[f\left(2\right)+3f\left(\frac{1}{2}\right)\right]-3\left[f\left(\frac{1}{2}\right)+3f\left(2\right)\right]=4-\frac{3}{4}\)
\(\Rightarrow-5f\left(2\right)=\frac{13}{4}\Leftrightarrow f\left(2\right)=-\frac{13}{20}\)
Ta có :
Thay x = 1/2 : ƒ (12 )+3ƒ (2)=14
Thay x = 2: ƒ (2)+3ƒ (12 )=4
⇒[ƒ (2)+3ƒ (12 )]−3[ƒ (12 )+3ƒ (2)]=4−34