Bài tập Toán DIFFERENTIATION OPTIMIZATION 06

Created by T Madas Question 15 (***+) The figure below shows a large tank in the shape of a cuboid with a rectangular base and no top Two of the vertical opposite faces of the cuboid are square and the height of the cuboid is x metres x a) Given that the surface area of the tank is 54 m , show that the capacity of the tank, V m3 , is given by V = 18 x − x3 b) Find the maximum value for V , fully justifying the fact that it is indeed the maximum value Vmax = 36 Created by T Madas Created by T Madas Question 16 (***+) x x x θ x x A wire of total length 60 cm is to be cut into two pieces The first piece is bent to form an equilateral triangle of side length x cm and the second piece is bent to form a circular sector of radius x cm The circular sector subtends an angle of θ radians at the centre a) Show that xθ = 60 − x The total area of the two shapes is A cm b) Show clearly that A= ( ) − 10 x + 30 x c) Use differentiation to find the value of x for which A is stationary d) Find, correct to three significant figures, the maximum value of A , justifying the fact that it is indeed the maximum value of A x ≈ 7.26 , Amax ≈ 109 Created by T Madas Created by T Madas Question 17 (****) 2x y The figure above shows the design of a theatre stage which is the shape of a semicircle attached to rectangle The diameter of the semicircle is x m and is attached to one side of the rectangle also measuring x m The other side of the rectangle is y m The perimeter of the stage is 60 m a) Show that the total area of the stage, A m , is given by A = 60 x − x − π x b) Show further, by using a differentiation method, that the maximum area of the stage is 1800 m2 π +4 proof Created by T Madas ... x The total area of the two shapes is A cm b) Show clearly that A= ( ) − 10 x + 30 x c) Use differentiation to find the value of x for which A is stationary d) Find, correct to three significant... the total area of the stage, A m , is given by A = 60 x − x − π x b) Show further, by using a differentiation method, that the maximum area of the stage is 1800 m2 π +4 proof Created by T Madas