CHO ( ) 2 ( )2MN TỐI GIẢN. TÍNH M−N2.A. M−N2 = −2018. B. M−N2 = −1....
Câu 35:
Cho
( )
2
( )
2
m
n
t
ố
i gi
ả
n. Tính
m
−
n
2
.
A.
m
−
n
2
= −
2018.
B.
m
−
n
2
= −
1.
C.
m
−
n
2
=
1.
D.
m
−
n
2
=
2018.
HD:
S
ử
d
ụ
ng
đẳ
ng th
ứ
c
1
1
1
1
1
1
1
1
+
+
+
= + −
+
⇒
+
+
+
= + −
+
=
v
ớ
i
x
>
0
1
1
1
1
x
x
x
x
x
x
x
x
g x
( )
2
2
( )
2
( )
2
2
1
1
( ) ( ) ( )
⇒
+
+ +
= + −
+ + −
+ + −
+ + +
−
g
g
g
1
2
...
2017
1
1
1
...
1
1
2
2
3
3
4
2017
2018
−
2
1
1
1
1
1
1
1
1
2018
1
=
+ − + − + − + +
−
=
+ −
=
2017
1
...
2017 1
2
2
3
3
4
2017
2018
2018
2018
+
+ +
−
( ) ( ) ( )
1 .
2 .
3 ...
(
2017
)
g
( ) ( )
1
g
2
...
g
(
2017
)
2018
2018
2
1
m
n
⇒
=
=
=
f
f
f
f
e
e
e
=
−
2018
2
1
⇒
=
2
1
⇒
m n
−
= −
.
Chọn B.
2018
n