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Bài tập CALCULUS 10

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Created by T. Madas
Question 38

(**+)

y

y = x2 − 5 x + 9
A

y =5

B

O

x

The figure above shows a quadratic curve and a straight line with respective equations

y = x2 − 5 x + 9

and

y = 5.

The points A and B are the points of intersection between the straight line and the
quadratic curve.

a) Find the coordinates of A and B .
b) Calculate the exact area of the finite region bounded by the quadratic curve and


the straight line, shown shaded in the above figure.
MP1-R , A (1,5 ) , B ( 4,5 ) , area = 9
2

Created by T. Madas


Created by T. Madas
Question 39

(**+)

The curve C with equation y = f ( x ) has gradient function
dy
7
= 9 x2 + 2 , x ≠ 0 .
dx
x
The point A ( −1, −1) lies on C .
Find an equation for C .
y = 3 x3 −

Question 40

7
−5
x

(**+)
y = 2x +


8
x2

, x ≠ 0.

Find the coordinates of the stationary point of y and determine its nature.
C2A , min ( 2,6 )

Created by T. Madas


Created by T. Madas
Question 41

(***)

24cm

x
64 cm

x

x

figure 2

figure 1


An open box is to be made out of a rectangular piece of card measuring 64 cm by
24 cm . Figure 1 shows how a square of side length x cm is to be cut out of each
corner so that the box can be made by folding, as shown in figure 2 .

a) Show that the volume of the box, V cm3 , is given by
V = 4 x3 − 176 x 2 + 1536 x .

b) Show further that the stationary points of V occur when
3 x 2 − 88 x + 384 = 0 .

c) Find the value of x for which V is stationary.
(You may find the fact 24 ×16 = 384 useful.)
d) Find, to the nearest cm3 , the maximum value for V , justifying that it is indeed
the maximum value.
x = 16 , Vmax ≈ 3793
3

Created by T. Madas



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