Có: \(f\left(x\right)=5x^3-7x^2+x+7\)

\(g\left(x\right)=7x^3+2x+5\)

\(h\left(x\right)=2x^3+4x+1\)

\(\Rightarrow k\left(x\right)=f\left(x\right)-g\left(x\right)+h\left(x\right)\\ =5x^3-7x^2+x+7-7x^3-2x-5+2x^3+4x+1\\ =\left(5x^3-7x^3+2x^3\right)+\left(7-5+1\right)+\left(4x-2x+x\right)-7x^2\\ =0+3+3x-7x^2\\ =-7x^2+3x+3\)

g= 35x²+15x-49x-21-35x²-28x+10x-8

g=-52x-(-29)

tại x=-3 ta có 

g= -52.(-3).(-29)

g=4542

\(G=\left(5x-7\right)\left(7x+3\right)-\left(7x+2\right)\left(5x-4\right)\)

\(=35x^2+15x-49x-21-35x^2+28x-10x+8\)

\(=-16x-13\)

Thay x = -3 \(\Rightarrow G=35\)

Vậy G = 35 khi x = -3

\(G=\left(5x-7\right)\left(7x+3\right)-\left(7x+2\right)\left(5x-4\right)\)

\(=\left(35x^2+15x-49x-21\right)-\left(35x^2-28x+10x-8\right)\)

\(=35x^2+15x-49x-21-35x^2+28x-10x+8\)

\(=-16x-13\)

Thay \(=-3\) vào biểu thức \(G\) , ta được :

\(G=-16x-13=-16\left(-3\right)-13=48-13=35\)

\(G=\left(5x-7\right)\left(7x+3\right)-\left(7x+2\right)\left(5x-4\right)\)

\(G=35x^2+15x-49x-21-\left(35x^2-28x+10x-8\right)\)

\(G=35x^2-34x-21-35x^2+18x+8\)

\(G=-16x-13\)(1)

Thay \(x=-3\) vào (1) ta được:

\(-16.\left(-3\right)-13=48-13=35\)

Vậy..............

Chúc bạn hcọ tốt!!!

`a,4x-10=0   `

`<=> 4x=10`

`<=>x=10/4`

`<=>x=5/2`

`b, 7-3x=9-x     `

`<=>-3x+x=9-7`

`<=>-2x=2`

`<=>x=-1`

`c, 2x-(3-5x) = 4(x+3)`

`<=>2x-3+5x=4x+12`

`<=>2x+5x-4x=12+3`

`<=>3x=15`

`<=>x=5`

`d, 5-(6-x)=4(3-2x)     `

`<=>5-6+x=12-8x`

`<=>x+8x=12-5+6`

`<=>9x=13`

`<=>x=13/9`

`e, 4(x+3)=-7x+17   `

`<=>4x+12=-7x+17`

`<=>4x+7x=17-12`

`<=>11x=5`

`<=>x=5/11`   

`f, 5(x-3) - 4=2(x-1)+7`

`<=>5x-15-4=2x-2+7`

`<=>5x-2x=15+4-2+7`

`<=>3x=24`

`<=>x=8`

`g, 5(x-3)-4=2(x-1)+7       `

`<=>5x-15-4=2x-2+7`

`<=>5x-2x=15+4-2+7`

`<=>3x=24`

`<=>x=8`

`h,4(3x-2)-3(x-4)=7x+20`

`<=>12x-8-3x+12=7x+20`

`<=>12x-3x-7x=20+8+12`

`<=>2x=40`

`<=>x=20`

a) \(f\left(x\right)=5x^3-7x^2+x+7+4x^5\)

\(f\left(-1\right)=5.\left(-1\right)^3-7.\left(-1\right)^2+\left(-1\right)+7+4.\left(-1\right)^5\)

\(f\left(-1\right)=\left(-5\right)-7+\left(-1\right)+7+\left(-4\right)\)

\(f\left(-1\right)=-10\)

\(\Rightarrow f\left(x\right)=-10\)

\(g\left(x\right)=4x^5-3x^3-7x^2+2x+5\)

\(g\left(0\right)=4.0^5-3.0^3-7.0^2+2.0+5\)

\(g\left(0\right)=5\)

\(\Rightarrow g\left(x\right)=0\)

\(h\left(x\right)=x^2-4x-5\)

\(h\left(-\frac{1}{2}\right)=\left(-\frac{1}{2}\right)^2-4.\left(-\frac{1}{2}\right)-5\)

\(h\left(-\frac{1}{2}\right)=\frac{1}{4}-\left(-2\right)-5\)

\(h\left(-\frac{1}{2}\right)=-\frac{11}{4}\)

\(\Rightarrow h\left(x\right)=-\frac{11}{4}\)

\(f\left(-1\right)=5\left(-1\right)^3-7\left(-1\right)^2+\left(-1\right)+7+4\left(-1\right)^5\)

\(f\left(-1\right)=-5-7-1+7-4\)

\(f\left(-1\right)=-10\)

\(g\left(0\right)=4.0^5-3.0^3-7.0^2+2.0+5\)

\(g\left(0\right)=0-0-0+0+5\)

\(g\left(0\right)=5\)

\(h\left(-\frac{1}{2}\right)=\left(-\frac{1}{2}\right)^2-4\left(-\frac{1}{2}\right)-5\)

\(h\left(-\frac{1}{2}\right)=\frac{1}{4}-\left(-2\right)-5\)

\(h\left(-\frac{1}{2}\right)=\frac{1}{4}+2-5\)

\(h\left(-\frac{1}{2}\right)=-\frac{11}{4}\)

a)f(x)+g(x)=\(x^5-4x^4-2x^2-7-2x^5+6x^4-2x^2+6.\)

=\(-x^5+2x^4-4x^2-1\)

f(x)-g(x)=\(x^5-4x^4-2x^2-7+2x^5-6x^4+2x^2-6\)

=\(3x^5-10x^4-13\)

b)f(x)+g(x)=\(5x^4+7x^3-6x^2+3x-7-4x^4+2x^3-5x^2+4x+5\)

=\(x^4+9x^3-11x^2+7x-2\)

f(x)-g(x)=\(5x^4+7x^3-6x^2+3x-7+4x^4-2x^3+5x^2-4x-5\)

=\(9x^4+5x^3-x^2-x-12\)

a ) 

\(f\left(x\right)+g\left(x\right)=x^5-4x^4-2x^2-7+-2x^5+6x^4-2x^2+6\)

\(\Rightarrow f\left(x\right)+g\left(x\right)=\left(x^5-2x^5\right)+\left(6x^4-4x^4\right)-\left(2x^2+2x^2\right)+\left(6-7\right)\)

\(\Rightarrow f\left(x\right)+g\left(x\right)=-x^5+2x^4-4x^2-1\)

\(f\left(x\right)-g\left(x\right)=x^5-4x^4-2x^2-7-\left(-2x^5+6x^4-2x^2+6\right)\)

\(\Rightarrow f\left(x\right)-g\left(x\right)=x^5-4x^4-2x^2-7+2x^5-6x^4+2x^2-6\)

\(\Rightarrow f\left(x\right)-g\left(x\right)=\left(x^5+2x^5\right)-\left(4x^4+6x^4\right)+\left(2x^2-2x^2\right)-\left(6+7\right)\)

\(\Rightarrow f\left(x\right)-g\left(x\right)=3x^5-10x^4-13\)

b ) Làm tương tự