ta có:  f(x) + g(x) = ( 7 x^6 - 6x ^5 +5x^4 -4x^3 +3x^2 -2x +1) - ( x - 2x^2 +3x^3 - 4x^4 + 5x^5 - 6x^6)

                          \(=7x^6-6x^5+5x^4-4x^3+3x^2-2x+1-x+2x^2-3x^3+4x^4-5x^5+6x^6\)

                      \(=\left(7x^6+6x^6\right)-\left(6x^5+5x^5\right)+\left(5x^4+4x^4\right)-\left(4x^3+3x^3\right)+\left(3x^2+2x^2\right)-\left(2x+x\right)+1\)

\(=13x^6-11x^5+9x^4-7x^3+5x^2-3x+1\)

Chúc bn học tốt !!!!!!

Uhhhhhhhhhhhhhhhhhhhhhhhhhh😥😥😥😥😥😥😥😥😥😥😥????????????...............

P(x)=2x^4-x-2x^3+1

Q(x)=5x^2-x^3+4x-8

tính h(x)=P+Q

 h(x)=P+Q=2x^4-x-2x^3+1+5x^2-x^3+4x-8

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

k(x)=Q-P=2x^4-x-2x^3+1-(5x^2-x^3+4x-8)

\(=2x^4-2x^3-x+1-5x^2+x^3-4x+8\)

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

ng công tỉnh lm nhầm câu b rồi nhưng thôi cx c.

ơn bn

để mk làm cho ; bài này dùng liên hợp

pt<=> \(x+1-\sqrt{x^2-2x+5}+2x+4-2\sqrt{4x+5}+x^3-2x^2+2x-1=0\) ( ĐKXĐ: \(x\ge-\frac{5}{4}\))

<=> \(\frac{x^2+2x+1-\left(x^2-2x+5\right)}{x+1+\sqrt{x^2-2x+5}}+\frac{\left(2x+4\right)^2-4\left(4x+5\right)}{2x+4+2\sqrt{4x+5}}+\left(x-1\right)\left(x^2-x+1\right)=0\)

<=>: \(\frac{x^2+2x+1-x^2+2x-5}{x+1+\sqrt{x^2-2x+5}}+\frac{4x^2+16x+16-16x-20}{2x+4+2\sqrt{4x+5}}+\left(x-1\right)\left(x^2-x+1\right)=0\)

<=> \(\frac{4x-4}{x+1+\sqrt{x^2-2x+5}}+\frac{4x^2-4}{2x+4+2\sqrt{4x+5}}+\left(x-1\right)\left(x^2-x+1\right)=0\)

<=> \(\left(x-1\right)\left(\frac{4}{x+1+\sqrt{x^2-2x+5}}+\frac{4x+4}{2x+4+2\sqrt{4x+5}}+x^2-x+1\right)=0\)

<=> x=1 ( vì \(x\ge-\frac{5}{4}\)nên cái trong ngoặc thứ 2 khác 0)

vậy x=1 

b) \(\frac{3\left(2x+1\right)}{4}-\frac{5x+3}{6}+\frac{x+1}{3}=\frac{x+7}{12}\)

<=> \(\frac{13\left(x+1\right)}{12}-\frac{5x+3}{6}=\frac{x+7}{12}\)

<=> 13(x + 1) - 2(5x + 3) = x + 7

<=> 13x + 13 - 10x - 6 = x + 7

<=> 3x + 7 = x + 7

<=> 3x + 7 - x = 7

<=> 2x + 7 = 7

<=> 2x = 7 - 7

<=> 2x = 0

<=> x = 0

c) 2x + 4(x - 2) = 5

<=> 2x + 4x - 8 = 5

<=> 6x - 8 = 5

<=> 6x = 5 + 8

<=> 6x = 13

<=> x = 13/6

Điều kiện x khác 0

     \(\left(5x^4-3x^3\right):2x^3=\frac{1}{2}\) 

\(\Rightarrow\frac{5}{2}x-\frac{3}{2}=\frac{1}{2}\)

\(\Rightarrow\frac{5}{2}x=2\Rightarrow x=\frac{4}{5}\)