Advertisements
Advertisements
Question
Find the maximum and minimum values of x + sin 2x on [0, 2π].
Advertisements
Solution
Let f (x) = x + sin2x, 0 ≤ x ≤ 2π
⇒ f' (x) = 1 + 2cos 2x
⇒ For critical points, let f' (x) = 0
⇒ 1 + cos 2x = 0
⇒ `cos 2x = -1/2`
⇒ `cos 2x = -cos pi/3`
(If 0< x < 2π, then 0< 2x < 4π)
`⇒ cos 2x = cos (pi- pi/3), cos (pi + pi/2), cos (3pi - pi/3), cos (3pi + pi/3)`
⇒ `2x = (2pi)/3 , (4pi)/3, (8pi)/3, (10pi)/3`
⇒ `x = pi/3, (2pi)/3, (4pi)/3, (5pi)/3`
So, for finding maximum and minimum, we evaluate f (x) at `0, 2pi , pi/3, (2pi)/3, (4pi)/3, (5pi)/3`
Now f(0) = 0 + sin 0 =
f (2π) = 2π + sin 4π = 2π + 0 = 2π
`f (pi/3) = pi/3 + sin (2pi)/3 = pi/3 + sin (pi - pi/3)`
= `pi/3 + sin pi/3 = pi/3 + sqrt3/2`
`f ((2pi)/3) = (2pi)/3 + sin (4pi)/3 = (2pi)/3 + sin (pi + pi/3)`
= `(2pi)/3 -sin pi/3 = (2pi)/3 - sqrt3/2`
`f((4pi)/3) = (4pi)/3 + sin (8pi)/3 = (4pi)/3 + sin (2pi + (2pi)/3)`
= `(4pi)/3 + sin (2pi)/3 = (4pi)/3 + sqrt3/2`
and `f ((5pi)/3) = (5pi)/3 + sin (10pi)/3 = (5pi)/3 + sin (3pi + pi/3)`
= `(5pi)/3 -sin pi/3 = (5pi)/3 - sqrt3/2`
Thus, maximum value of f (x) = 2π at x = 2π and minimum value of f (x) = 0 at x = 0.
APPEARS IN
RELATED QUESTIONS
If `f'(x)=k(cosx-sinx), f'(0)=3 " and " f(pi/2)=15`, find f(x).
Find the maximum and minimum value, if any, of the following function given by f(x) = 9x2 + 12x + 2
Find the local maxima and local minima, if any, of the following function. Find also the local maximum and the local minimum values, as the case may be:
g(x) = x3 − 3x
Prove that the following function do not have maxima or minima:
g(x) = logx
Find the absolute maximum value and the absolute minimum value of the following function in the given interval:
`f(x) = 4x - 1/x x^2, x in [-2 ,9/2]`
Find the maximum profit that a company can make, if the profit function is given by p(x) = 41 − 72x − 18x2.
Find two numbers whose sum is 24 and whose product is as large as possible.
Find two positive numbers whose sum is 16 and the sum of whose cubes is minimum.
Show that the right circular cylinder of given surface and maximum volume is such that is heights is equal to the diameter of the base.
The maximum value of `[x(x −1) +1]^(1/3)` , 0 ≤ x ≤ 1 is ______.
A window is in the form of a rectangle surmounted by a semicircular opening. The total perimeter of the window is 10 m. Find the dimensions of the window to admit maximum light through the whole opening
Find the points at which the function f given by f (x) = (x – 2)4 (x + 1)3 has
- local maxima
- local minima
- point of inflexion
Show that the altitude of the right circular cone of maximum volume that can be inscribed in a sphere of radius r is `(4r)/3.`
A metal box with a square base and vertical sides is to contain 1024 cm3. The material for the top and bottom costs Rs 5 per cm2 and the material for the sides costs Rs 2.50 per cm2. Find the least cost of the box
Show that a cylinder of a given volume, which is open at the top, has minimum total surface area when its height is equal to the radius of its base.
The volume of a closed rectangular metal box with a square base is 4096 cm3. The cost of polishing the outer surface of the box is Rs. 4 per cm2. Find the dimensions of the box for the minimum cost of polishing it.
Find the maximum and minimum of the following functions : y = 5x3 + 2x2 – 3x.
Find the maximum and minimum of the following functions : f(x) = `x^2 + (16)/x^2`
Divide the number 20 into two parts such that sum of their squares is minimum.
A ball is thrown in the air. Its height at any time t is given by h = 3 + 14t – 5t2. Find the maximum height it can reach.
State whether the following statement is True or False:
An absolute maximum must occur at a critical point or at an end point.
Find the local maximum and local minimum value of f(x) = x3 − 3x2 − 24x + 5
If f(x) = px5 + qx4 + 5x3 - 10 has local maximum and minimum at x = 1 and x = 3 respectively then (p, q) = ______.
Twenty meters of wire is available for fencing off a flowerbed in the form of a circular sector. Then the maximum area (in sq. m) of the flower-bed, is ______
A telephone company in a town has 500 subscribers on its list and collects fixed charges of Rs 300/- per subscriber per year. The company proposes to increase the annual subscription and it is believed that for every increase of Re 1/- one subscriber will discontinue the service. Find what increase will bring maximum profit?
A ball is thrown upward at a speed of 28 meter per second. What is the speed of ball one second before reaching maximum height? (Given that g= 10 meter per second2)
Range of projectile will be maximum when angle of projectile is
The function `f(x) = x^3 - 6x^2 + 9x + 25` has
If S1 and S2 are respectively the sets of local minimum and local maximum points of the function. f(x) = 9x4 + 12x3 – 36x2 + 25, x ∈ R, then ______.
A cone of maximum volume is inscribed in a given sphere. Then the ratio of the height of the cone to the diameter of the sphere is ______.
The greatest value of the function f(x) = `tan^-1x - 1/2logx` in `[1/sqrt(3), sqrt(3)]` is ______.
A straight line is drawn through the point P(3, 4) meeting the positive direction of coordinate axes at the points A and B. If O is the origin, then minimum area of ΔOAB is equal to ______.
Sum of two numbers is 5. If the sum of the cubes of these numbers is least, then find the sum of the squares of these numbers.
Find the maximum profit that a company can make, if the profit function is given by P(x) = 72 + 42x – x2, where x is the number of units and P is the profit in rupees.
If x + y = 8, then the maximum value of x2y is ______.
Find the point on the curve y2 = 4x, which is nearest to the point (2, 1).
A box with a square base is to have an open top. The surface area of box is 147 sq. cm. What should be its dimensions in order that the volume is largest?
