Toán Lớp 7: (x) = x^3 (3x –1) – x (l + 3x^4); g(x) = x^2 (x^2 + 2) – x (–x^4 + 2x^2 +7) + 3; h(x) = x^3 (–2 + 2x – x^2) – (5x – 3 – 2x^2) a) Thu g

Question

Toán Lớp 7:  (x) = x^3 (3x –1) – x (l + 3x^4); g(x) = x^2 (x^2 + 2) – x (–x^4 + 2x^2 +7) + 3; h(x) = x^3 (–2 + 2x – x^2) –  (5x – 3 – 2x^2) a) Thu gọn rồi sắp xếp các hạng tử của mỗi đa thức trên theo lũy thừa giảm dần của biến. b) Tính A(x) =   (x) + g(x) – 2h(x).

giangnguyen33 · Answer

a,   (x)=x&sup3;(3x-1)-x(1+3$x^{4}$ )   =3$x^{4}$ -x&sup3;-x-3$x^{5}$    =-3$x^{5}$+3$x^{4}$-x&sup3;-x;   g(x)=$x^{4}$+2x&sup2;+$x^{5}$ -2x&sup3;-7x+3   =$x^{5}$+$x^{4}$-2x&sup3;+2x&sup2;-7x+3   h(x)=-2x&sup3;+2$x^{4}$ -$x^{5}$-5x+3+2x&sup2;   =-$x^{5}$+2$x^{4}$-2x&sup3;+2x&sup2;-5x+3   b,           (x)= 3$x^{5}$+3$x^{4}$-  x&sup3;-           x   +    g(x)=   $x^{5}$+  $x^{4}$-2x&sup3;+2x&sup2;- 7x+3   -   2h(x)=-2$x^{5}$+4$x^{4}$-4x&sup3;+4x&sup2;-10x+6   ------------------------------------------------         A(x)= 6$x^{5}$+0              +x&sup3;-2x&sup2;+4x-3

diemchau · Answer

Giải đáp:       Lời giải và giải thích chi tiết:   ${a,}$   ${(x) = x^3 (3x &ndash;1) &ndash; x (1 + 3x^4)}$   ${(x)= 3x^4 &ndash; x^3 -x +3x^4}$   ${(x)= 6x^4 &ndash; x^3 -x }$   ${g(x) = x^2 (x^2 + 2) &ndash; x (&ndash;x^4 + 2x^2 +7) + 3}$   ${g(x)=x^4 + 2x^2 + x^5 -2x^3 -7x +3}$   ${g(x)= x^5 +x^4 -2x^3 + 2x^2 - 7x +3}$   ${h(x) = x^3 (&ndash;2 + 2x &ndash; x^2) &ndash; (5x &ndash; 3 &ndash; 2x^2)}$   ${h(x) = -2x^3 + 2x^4 -x^5 -5x +3+2x^2}$   ${h(x) = -x^5 + 2x^4 -2x^3 +2x^2 - 5x + 3 }$   ${b,}$   ${A(x) = (x) + g(x) &ndash; 2h(x)}$   ${A(x) = (6x^4 &ndash; x^3 -x) + (x^5 +x^4 -2x^3 + 2x^2 - 7x +3) - 2.(-x^5 + 2x^4 -2x^3 +2x^2 - 5x + 3)}$   ${A(x) = (6x^4 &ndash; x^3 -x) + (x^5 +x^4 -2x^3 + 2x^2 - 7x +3) + 2x^5 - 4x^4 + 4x^3 - 4x^2 + 10x - 6}$   ${A(x) = 6x^4 &ndash; x^3 -x + x^5 +x^4 -2x^3 + 2x^2 - 7x +3 + 2x^5 - 4x^4 + 4x^3 - 4x^2 + 10x - 6}$   ${A(x) = 6x^4 &ndash; x^3 -x + x^5 +x^4 -2x^3 + 2x^2 - 7x +3 + 2x^5 - 4x^4 + 4x^3 - 4x^2 + 10x - 6}$   ${A(x) =(x^5 + 2x^5) + (6x^4 + x^4- 4x^4) + (&ndash; x^3 -2x^3+ 4x^3) + (2x^2- 4x^2)+(-x- 7x + 10x) +(3- 6)}$   ${A(x) = 3x^5 + 3x^4 + x^3 - 2x^2 + 2x - 3 }$