## Wednesday, 15 September 2010

### Question on variations

F.4,5 level? yeah~
Question 1 direct variations
a)For each of the following conditions, does it imply that x is directly proportional to y? Assume x,y are real.
i)x^2 varies directly to y^2. (4M)
ii)x^3 varies directly to y^2. (4M)
iii)log x varies directly to log y. (5M + 1 Bonus)
iv)tan x varies directly to tan y. (5M + 2 Bonus)
v)sin x varies directly to cos y. (5M + 2 Bonus)
b)In a more general way, when does x proportional to y if f(x) varies to f(y) is given? Explain your answer in terms of:
i)Algebrical method (11M)
ii)Geometry apporach (15M)
Question 2 partial variations
a)State the nature of functions that is used in partial variations. (3M)
b)If the function is symmetrical, what's its special properties? Explain. (6M + 1 Bonus)
c)If the function is cyclic, what's its special properties? Explain. (8M + 1 Bonus)
d)If the function is alternative, what's its special properties? Explain. (6M + 1 Bonus)
e)If f'(x) is directly proportional to f'(y) where f is a polynomial, find the corresponding types of variation between x and y. (7M)
f)For the relationship x=f(y,z), where f is a polyomial, find the relationship between x and (δf/δy+δf/δz). (13M)
Full marks: 100 Time limits : 75 minutes or 1.5 hour