Bài 6:
\(F\left(x\right)=2x-x^2-2\left(x+1\right)=2x-x^2-2x-2=-x^2-2\\ F\left(-\dfrac{3}{2}\right)=-\left(-\dfrac{3}{2}\right)^2-2=-\dfrac{9}{4}-2=-\dfrac{17}{4}\)
Bài 7:
\(f\left(1\right)=-a+b=-15\Rightarrow b=-15+a\\ f\left(2\right)=2a+b=-9\Rightarrow b=-9-2a\\ Vậy:a-15=-9-2a\\ \Leftrightarrow a+2a=15-9\\ \Leftrightarrow3a=6\Leftrightarrow a=2\Rightarrow b=-9-2a=-13\\ Vậy:y=f\left(x\right)=8x-13\)
Bài 4:
\(Tại.x=-1:\\ ax^3+bx^2+cx+d=a\left(-1\right)^3+b\left(-1\right)^2+c.\left(-1\right)+d=-a+b-c+d\)
Bài 5:
\(P\left(x\right)=5.x^{100}+5.x^{99}+5.x^{98}+...+5.x+9\\ =5\left(x^{100}+x^{99}+x^{98}+...+x\right)+9\\ P\left(1\right)=5.\left(1-1+1-1+....+1-1\right)+9\\ =5.0+9=0+9=9\)
6:
F=2x-x^2-2x-2=-x^2-2
=-(-3/2)^2-2=-3/4-2=-11/4
7:
f(-1)=-15 và f(2)=-9
=>-a+b=-15 và 2a+b=-9
=>a=2 và b=-13
