y is the sum of two parts. One part varies directly as x, while the other part varies directly as x^2. y=-33 when x=3 and y=-48 when x=6.
(a) Express y in terms of x. Hence find the value of y when x=16
(b) Find the minimum possible value of y when x varies.
F.4 variations---
2010-01-29 10:00 pm
回答 (1)
2010-01-29 10:17 pm
✔ 最佳答案
(a)let y=ax+bx^2,where a and b is constant.
Putting y=33,x=3 .
y=-48, x=6.
By solving, we have
a=-14
b=1
So,y=-14x+x^2
Putting x=16
y=-14(16)+16^2
=32
(b)
y=x^2-14x
=(x-7)^2-49
So,y is minimum when x=7
y=-49
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