Đáp án:
$3)
A=75\\
B=\dfrac{-391}{4}\\
C=-6\\
D=37\\
E=24\\
F=\dfrac{5}{4}$
Giải thích các bước giải:
$3)
A=5x(x^2-3)+x^2(7-5x)-7x^2\\
=5x^3-15x+7x^2-5x^3-7x^2\\
=(5x^3-5x^3)+(7x^2-7x^2)-15x\\
=-15x\\
\Rightarrow A(-5)=(-15).(-5)=75\\
B=x(x-y)+y(x-y)\\
=x^2-xy+xy-y^2\\
=x^2-y^2\\
\Rightarrow B(1,5;10)=(1,5)^2-10^2=\dfrac{-391}{4}\\
C=7x(x-5)+3(x-2)\\
=7x^2-35x+3x-6\\
=7x^2-32x-6\\
\Rightarrow C(0)=7.0-32.0-6=-6\\
D=5-4x(x-2)+4x^2\\
=5-4x^2+8x+4x^2\\
=8x+5\\
\Rightarrow D(4)=8.4+5=37\\
E=4x^2-2x+3x(x-5)\\
=4x^2-2x+3x^2-15x\\
=7x^2-17x\\
\Rightarrow E(-1)=7.(-1)^2-17.(-1)=7+17=24\\
F=(5x-7)(2x+3)-(7x+2)(x-4)\\
=10x^2+15x-14x-21-(7x^2-28x+2x-8)\\
=10x^2+15x-14x-21-7x^2+28x-2x+8\\
=(10x^2-7x^2)+(15x-14x+28x-2x)+(-21+8)\\
=3x^2+27x-13\\
\Rightarrow F(\dfrac{1}{2})=3.\left ( \dfrac{1}{2} \right )^2+27.\dfrac{1}{2}-13=\dfrac{5}{4}$
