Question

Answer 1

a, Thay \(x=2;y=9\) vào A ta có:

\(A=2x^2-\dfrac{1}{3}y=2.2^2-\dfrac{1}{3}.9=8-3=5\)

b, Thay \(a=-2;b=-\dfrac{1}{3}\) vào B ta có:

\(B=\dfrac{1}{2}a^2-3b^2=\dfrac{1}{2}.\left(-2\right)^2-3.\left(-\dfrac{1}{3}\right)^2=2-\dfrac{1}{3}=\dfrac{5}{3}\)

c, Thay \(x=-\dfrac{1}{2};y=\dfrac{2}{3}\) vào P ta có:

\(P=2x^2+3xy+y^2=2.\left(-\dfrac{1}{2}\right)^2+3.\left(-\dfrac{1}{2}\right).\dfrac{2}{3}+\left(\dfrac{2}{3}\right)^2=\dfrac{1}{2}-1+\dfrac{4}{9}=-\dfrac{1}{18}\)

d, Thay \(a=-\dfrac{1}{3}b=-\dfrac{1}{6}\) vào D ta có:

\(D=12ab^2=12.\left(-\dfrac{1}{3}\right).\left(-\dfrac{1}{6}\right)^2=-\dfrac{1}{9}\)

Answer 2

a, Thay 
x
=
2
;
y
=
9
 vào A ta có:

A
=
2
x
2
−
1
3
y
=
2.2
2
−
1
3
.9
=
8
−
3
=
5

b, Thay 
a
=
−
2
;
b
=
−
1
3
 vào B ta có:

B
=
1
2
a
2
−
3
b
2
=
1
2
.
(
−
2
)
2
−
3.
(
−
1
3
)
2
=
2
−
1
3
=
5
3

c, Thay 
x
=
−
1
2
;
y
=
2
3
 vào P ta có:

P
=
2
x
2
+
3
x
y
+
y
2
=
2.
(
−
1
2
)
2
+
3.
(
−
1
2
)
.
2
3
+
(
2
3
)
2
=
1
2
−
1
+
4
9
=
−
1
18

d, Thay 
a
=
−
1
3
b
=
−
1
6
 vào D ta có:

D
=
12
a
b
2
=
12.
(
−
1
3
)
.
(
−
1
6
)
2
=
−
1
9