3. Inequality Techniques
To prove x y, it can be easier to prove x y 0
p2 q2
e.g. i 1995 Prove pq
2
4. Inequality Techniques
To prove x y, it can be easier to prove x y 0
p2 q2
e.g. i 1995 Prove pq
2
p2 q2
pq
2
5. Inequality Techniques
To prove x y, it can be easier to prove x y 0
p2 q2
e.g. i 1995 Prove pq
2
p2 q2 p 2 2 pq q 2
pq
2 2
6. Inequality Techniques
To prove x y, it can be easier to prove x y 0
p2 q2
e.g. i 1995 Prove pq
2
p2 q2 p 2 2 pq q 2
pq
2 2
p q 2
2
7. Inequality Techniques
To prove x y, it can be easier to prove x y 0
p2 q2
e.g. i 1995 Prove pq
2
p2 q2 p 2 2 pq q 2
pq
2 2
p q 2
2
0
8. Inequality Techniques
To prove x y, it can be easier to prove x y 0
p2 q2
e.g. i 1995 Prove pq
2
p2 q2 p 2 2 pq q 2
pq
2 2
p q2
2
0
p2 q2
pq
2
10. ii 1994 a) Prove a 2 b 2 c 2 ab bc ac
a b 2 0
11. ii 1994 a) Prove a 2 b 2 c 2 ab bc ac
a b 2 0
a 2 2ab b 2 0
12. ii 1994 a) Prove a 2 b 2 c 2 ab bc ac
a b 2 0
a 2 2ab b 2 0
a 2 b 2 2ab
13. ii 1994 a) Prove a 2 b 2 c 2 ab bc ac
a b 2 0
a 2 2ab b 2 0
a 2 b 2 2ab
a 2 c 2 2ac
b 2 c 2 2bc
14. ii 1994 a) Prove a 2 b 2 c 2 ab bc ac
a b 2 0
a 2 2ab b 2 0
a 2 b 2 2ab
a 2 c 2 2ac
b 2 c 2 2bc
2a 2 2b 2 2c 2 2ab 2ac 2bc
15. ii 1994 a) Prove a 2 b 2 c 2 ab bc ac
a b 2 0
a 2 2ab b 2 0
a 2 b 2 2ab
a 2 c 2 2ac
b 2 c 2 2bc
2a 2 2b 2 2c 2 2ab 2ac 2bc
a 2 b 2 c 2 ab ac bc
16. ii 1994 a) Prove a 2 b 2 c 2 ab bc ac
a b 2 0
a 2 2ab b 2 0
a 2 b 2 2ab
a 2 c 2 2ac
b 2 c 2 2bc
2a 2 2b 2 2c 2 2ab 2ac 2bc
a 2 b 2 c 2 ab ac bc
1
b) If a b c 1, prove ab ac bc
3
17. ii 1994 a) Prove a 2 b 2 c 2 ab bc ac
a b 2 0
a 2 2ab b 2 0
a 2 b 2 2ab
a 2 c 2 2ac
b 2 c 2 2bc
2a 2 2b 2 2c 2 2ab 2ac 2bc
a 2 b 2 c 2 ab ac bc
1
b) If a b c 1, prove ab ac bc
3
a b c a b c 2ab ac bc
2 2 2 2
18. ii 1994 a) Prove a 2 b 2 c 2 ab bc ac
a b 2 0
a 2 2ab b 2 0
a 2 b 2 2ab
a 2 c 2 2ac
b 2 c 2 2bc
2a 2 2b 2 2c 2 2ab 2ac 2bc
a 2 b 2 c 2 ab ac bc
1
b) If a b c 1, prove ab ac bc
3
a b c a b c 2ab ac bc
2 2 2 2
a b c 2ab ac bc ab ac bc
2
19. ii 1994 a) Prove a 2 b 2 c 2 ab bc ac
a b 2 0
a 2 2ab b 2 0
a 2 b 2 2ab
a 2 c 2 2ac
b 2 c 2 2bc
2a 2 2b 2 2c 2 2ab 2ac 2bc
a 2 b 2 c 2 ab ac bc
1
b) If a b c 1, prove ab ac bc
3
a b c a b c 2ab ac bc
2 2 2 2
a b c 2ab ac bc ab ac bc
2
3ab ac bc a b c
2
20. ii 1994 a) Prove a 2 b 2 c 2 ab bc ac
a b 2 0
a 2 2ab b 2 0
a 2 b 2 2ab
a 2 c 2 2ac
b 2 c 2 2bc
2a 2 2b 2 2c 2 2ab 2ac 2bc
a 2 b 2 c 2 ab ac bc
1
b) If a b c 1, prove ab ac bc
3
a b c a b c 2ab ac bc
2 2 2 2
a b c 2ab ac bc ab ac bc
2
3ab ac bc a b c
2
3ab ac bc 1
1
ab ac bc
3
22. 1
c) Prove a b c 3 abc
3
a 2 b 2 c 2 ab ac bc
23. 1
c) Prove a b c 3 abc
3
a 2 b 2 c 2 ab ac bc
a 2 b 2 c 2 ab ac bc 0
24. 1
c) Prove a b c 3 abc
3
a 2 b 2 c 2 ab ac bc
a 2 b 2 c 2 ab ac bc 0
a b c a 2 b 2 c 2 ab ac bc 0
25. 1
c) Prove a b c 3 abc
3
a 2 b 2 c 2 ab ac bc
a 2 b 2 c 2 ab ac bc 0
a b c a 2 b 2 c 2 ab ac bc 0
a 3 ab 2 ac 2 a 2b a 2 c abc a 2b b 3 bc 2 ab 2 abc b 2 c
a 2 c b 2 c c 3 abc ac 2 bc 2 0
26. 1
c) Prove a b c 3 abc
3
a 2 b 2 c 2 ab ac bc
a 2 b 2 c 2 ab ac bc 0
a b c a 2 b 2 c 2 ab ac bc 0
a 3 ab 2 ac 2 a 2b a 2 c abc a 2b b 3 bc 2 ab 2 abc b 2 c
a 2 c b 2 c c 3 abc ac 2 bc 2 0
a 3 b 3 c 3 3abc 0
27. 1
c) Prove a b c 3 abc
3
a 2 b 2 c 2 ab ac bc
a 2 b 2 c 2 ab ac bc 0
a b c a 2 b 2 c 2 ab ac bc 0
a 3 ab 2 ac 2 a 2b a 2 c abc a 2b b 3 bc 2 ab 2 abc b 2 c
a 2 c b 2 c c 3 abc ac 2 bc 2 0
a 3 b 3 c 3 3abc 0
a b c abc
1 3 3 3
3
28. 1
c) Prove a b c 3 abc
3
a 2 b 2 c 2 ab ac bc
a 2 b 2 c 2 ab ac bc 0
a b c a 2 b 2 c 2 ab ac bc 0
a 3 ab 2 ac 2 a 2b a 2 c abc a 2b b 3 bc 2 ab 2 abc b 2 c
a 2 c b 2 c c 3 abc ac 2 bc 2 0
a 3 b 3 c 3 3abc 0
a b c abc
1 3 3 3
3
1 1 1
let a a , b b , c c
3 3 3
29. 1
c) Prove a b c 3 abc
3
a 2 b 2 c 2 ab ac bc
a 2 b 2 c 2 ab ac bc 0
a b c a 2 b 2 c 2 ab ac bc 0
a 3 ab 2 ac 2 a 2b a 2 c abc a 2b b 3 bc 2 ab 2 abc b 2 c
a 2 c b 2 c c 3 abc ac 2 bc 2 0
a 3 b 3 c 3 3abc 0
a b c abc
1 3 3 3
3
1 1 1
let a a , b b , c c
3 3 3
1 1 1
1
a b c a 3 b 3 c 3
3
30. 1
c) Prove a b c 3 abc
3
a 2 b 2 c 2 ab ac bc
a 2 b 2 c 2 ab ac bc 0
a b c a 2 b 2 c 2 ab ac bc 0
a 3 ab 2 ac 2 a 2b a 2 c abc a 2b b 3 bc 2 ab 2 abc b 2 c
a 2 c b 2 c c 3 abc ac 2 bc 2 0
a 3 b 3 c 3 3abc 0
a b c abc
1 3 3 3
3
1 1 1
let a a , b b , c c
3 3 3
1 1 1
1
a b c a 3 b 3 c 3
3
1
a b c 3 abc
3
32. Arithmetic Mean Geometric Mean
a1 a2 an n
a1a2 an
n
d) Suppose 1 x 1 y 1 z 8, prove xyz 1
33. Arithmetic Mean Geometric Mean
a1 a2 an n
a1a2 an
n
d) Suppose 1 x 1 y 1 z 8, prove xyz 1
1 x 1 y 1 z 8
1 x y xy z xz yz xyz 8
34. Arithmetic Mean Geometric Mean
a1 a2 an n
a1a2 an
n
d) Suppose 1 x 1 y 1 z 8, prove xyz 1
1 x 1 y 1 z 8
1 x y xy z xz yz xyz 8
1
x y z 3 xyz
3
35. Arithmetic Mean Geometric Mean
a1 a2 an n
a1a2 an
n
d) Suppose 1 x 1 y 1 z 8, prove xyz 1
1 x 1 y 1 z 8
1 x y xy z xz yz xyz 8
1
x y z 3 xyz
3
x y z 33 xyz
36. Arithmetic Mean Geometric Mean
a1 a2 an n
a1a2 an
n
d) Suppose 1 x 1 y 1 z 8, prove xyz 1
1 x 1 y 1 z 8
1 x y xy z xz yz xyz 8
1
x y z 3 xyz
3
x y z 33 xyz
xy yz xz 33 xy yz xz
37. Arithmetic Mean Geometric Mean
a1 a2 an n
a1a2 an
n
d) Suppose 1 x 1 y 1 z 8, prove xyz 1
1 x 1 y 1 z 8
1 x y xy z xz yz xyz 8
1
x y z 3 xyz
3
x y z 33 xyz
xy yz xz 33 xy yz xz
xy yz xz 33 x 2 y 2 z 2
38. Arithmetic Mean Geometric Mean
a1 a2 an n
a1a2 an
n
d) Suppose 1 x 1 y 1 z 8, prove xyz 1
1 x 1 y 1 z 8
1 x y xy z xz yz xyz 8
1
x y z 3 xyz
3
x y z 33 xyz
xy yz xz 33 xy yz xz
xy yz xz 33 x 2 y 2 z 2
xy yz xz 3 xyz
2
3