a) 

\(P=\left(x^{14}-9x^{13}\right)-\left(x^{13}-9x^{12}\right)+\left(x^{12}-9x^{11}\right)-...+\left(x^2-9x\right)-\left(x-9\right)+1\)

\(=x^{13}\left(x-9\right)-x^{12}\left(x-9\right)+x^{11}\left(x-9\right)+...+x\left(x-9\right)-\left(x-9\right)+1\)

\(P\left(9\right)=1\)

b)

\(Q=\left(x^{15}-7x^{14}\right)-\left(x^{14}-7x^{13}\right)+\left(x^{13}-7x^{12}\right)-...-\left(x^2-7x\right)+\left(x-7\right)+2\)

\(=x^{14}\left(x-7\right)-x^{13}\left(x-7\right)+x^{12}\left(x-7\right)-...-x\left(x-7\right)+\left(x-7\right)+2\)

\(Q\left(7\right)=2\)

\(Q_{\left(x\right)}=x^{14}-10x^{13}+10x^{12}-10x^{11}+...+10x^2-10x+10\)

\(=x^{14}-\left(x+1\right)x^{13}+\left(x+1\right)x^{12}-\left(x+1\right)x^{11}+..+\left(x+1\right)x^2-\left(x+1\right)x+x+1\)

\(=x^{14}-x^{14}-x^{13}+x^{13}+x^{12}-x^{12}-x^{11}+...+x^3+x^2-x^2-x+x+1\)

\(=1\)

\(a.P(x)=x^7-80x^6+80x^5-80x^4+....+80x+15\)

\(=x^7-79x^6-x^6+79x^5+x^5-79x^4-....-x^2+79x+x+15\)

\(=x^6(x-79)-x^5(x-79)+x^4(x-79)-....-x(x-79)+x+15\)

\(=(x-79)(x^6-x^5+x^4-....-x)+x+15\)

Thay x = 79 vào biểu thức trên , ta có

\(P(79)=(79-79)(79^6-79^5+79^4-...-79)+79+15\)

\(=0+79+15\)

\(=94\)

Vậy \(P(x)=94\)khi x = 79

\(b.Q(x)=x^{14}-10x^{13}+10x^{12}-.....+10x^2-10x+10\)

\(=x^{14}-9x^{13}-x^{13}+9x^{12}+.....-x^3+9x^2+x^2-9x-x+10\)

\(=x^{13}(x-9)-x^{12}(x-9)+.....-x^2(x-9)+x(x-9)-x+10\)

\(=(x-9)(x^{13}-x^{12}+.....-x^2+x)-x+10\)

Thay x = 9 vào biểu thức trên , ta có

\(Q(9)=(9-9)(9^{13}-9^{12}+.....-9^2+9)-9+10\)

\(=0-9+10\)

\(=1\)

Vậy \(Q(x)=1\)khi x = 9

\(c.R(x)=x^4-17x^3+17x^2-17x+20\)

\(=x^4-16x^3-x^3+16x^2+x^2-16x-x+20\)

\(=x^3(x-16)-x^2(x-16)+x(x-16)-x+20\)

\(=(x-16)(x^3-x^2+x)-x+20\)

Thay x = 16 vào biểu thức trên , ta có

\(R(16)=(16-16)(16^3-16^2+16)-16+20\)

\(=0-16+20\)

\(=4\)

Vậy \(R(x)=4\)khi x = 16

\(d.S(x)=x^{10}-13x^9+13x^8-13x^7+.....+13x^2-13x+10\)

\(=x^{10}-12x^9-x^9+12x^8+.....+x^2-12x-x+10\)

\(=x^9(x-12)-x^8(x-12)+....+x(x-12)-x+10\)

\(=(x-12)(x^9-x^8+....+x)-x+10\)

Thay x = 12 vào biểu thức trên , ta có

\(S(12)=(12-12)(12^9-12^8+....+12)-12+10\)

\(=0-12+10\)

\(=-2\)

Vậy \(S(x)=-2\)khi x = 12

Hình như đây là toán lớp 7 có trong phần trắc nghiệm của thi HSG huyện

Chúc bạn học tốt , nhớ kết bạn với mình

em chịu_{em thua}

cái gì đây?

của bạn nè.Mik lớp 5 nhưng vẫn phải học thuộc hết 

\(a,=x\left(x^2-10x+25\right)=x\left(x-5\right)^2\\ b,=y\left(x+y\right)-\left(x+y\right)=\left(y-1\right)\left(x+y\right)\\ c,=\left(x-5\right)^2\\ d,=\left(x-8\right)\left(x+8\right)\)

\(x=9\Leftrightarrow x+1=10\\ \Leftrightarrow M=x^{2012}-\left(x+1\right)x^{2012}+...-\left(x+1\right)x^2+\left(x+1\right)x-\left(x+1\right)\\ M=x^{2012}-x^{2013}-x^{2012}+...-x^3-x^2+x^2+x-x-1\\ \Leftrightarrow M=-x^{2013}-1=-9^{2013}-1\)

\(=\dfrac{7}{10}\times\left(3+5+2\right)=\dfrac{7}{10}\times10=7\)

giúp mình với

7/10x3 + 7/10 x5 +7/10x2=7/10x(3+5+2)

                                         =7/10x10

                                         =7

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