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# Question Paper Solutions - Mathematics 2012 - 2013 CBSE (Commerce) Class 12

SubjectMathematics
Year2012 - 2013 (March)

Marks: 100
[1]1

Write the principal value of tan^(-1)+cos^(-1)(-1/2)

Chapter: [1.02] Inverse Trigonometric Functions
Concept: Inverse Trigonometric Functions - Inverse Trigonometric Functions - Principal Value Branch
[1]2

Write the value of tan(2tan^(-1)(1/5))

Chapter: [1.02] Inverse Trigonometric Functions
Concept: Inverse Trigonometric Functions (Simplification and Examples)
[1]3

Find the value of a if [[a-b,2a+c],[2a-b,3c+d]]=[[-1,5],[0,13]]

Chapter: [2.02] Determinants
Concept: Applications of Determinants and Matrices
[1]4

If |[x+1,x-1],[x-3,x+2]|=|[4,-1],[1,3]|, then write the value of x.

Chapter: [2.02] Determinants
Concept: Applications of Determinants and Matrices
[1]5

if [[9,-1,4],[-2,1,3]]=A+[[1,2,-1],[0,4,9]], then find the matrix A.

Chapter: [2.01] Matrices
Concept: Subtraction of Matrices
[1]6

Write the degree of the differential equation x^3((d^2y)/(dx^2))^2+x(dy/dx)^4=0

Chapter: [3.05] Differential Equations
Concept: Order and Degree of a Differential Equation
[1]7

If veca=xhati+2hatj-zhatk and vecb=3hati-yhatj+hatk are two equal vectors ,then write the value of x+y+z

Chapter: [4.01] Vectors
Concept: Types of Vectors
[1]8

If a unit vector veca makes angles pi/3 with hati,pi/4 with hatj and acute angles θ with  hatk, then find the value of θ.

Chapter: [4.01] Vectors
Concept: Vectors Examples and Solutions
[1]9

Find the Cartesian equation of the line which passes through the point (−2, 4, −5) and is parallel to the line (x+3)/3=(4-y)/5=(z+8)/6

Chapter: [4.02] Three - Dimensional Geometry
Concept: Equation of a Line in Space
[1]10

The amount of pollution content added in air in a city due to x-diesel vehicles is given by P(x) = 0.005x3 + 0.02x2 + 30x. Find the marginal increase in pollution content when 3 diesel vehicles are added and write which value is indicated in the above question.

Chapter: [3.02] Applications of Derivatives
Concept: Increasing and Decreasing Functions
[4]11

Show that the function f in A=R-{2/3}  defined as f(x)=(4x+3)/(6x-4) is one-one and onto hence find f-1

Chapter: [1.01] Relations and Functions
Concept: Types of Functions
[4]12 | Attempt any one of the following
[4]12.1

Find the value of the following: tan(1/2)[sin^(-1)((2x)/(1+x^2))+cos^(-1)((1-y^2)/(1+y^2))],|x| <1,y>0 and xy <1

Chapter: [1.02] Inverse Trigonometric Functions
Concept: Inverse Trigonometric Functions (Simplification and Examples)
[4]12.2

Prove that: tan^(-1)(1/2)+tan^(-1)(1/5)+tan^(-1)(1/8)=pi/4

Chapter: [1.02] Inverse Trigonometric Functions
Concept: Properties of Inverse Trigonometric Functions
[4]13

Using properties of determinants prove the following: |[1,x,x^2],[x^2,1,x],[x,x^2,1]|=(1-x^3)^2

Chapter: [2.02] Determinants
Concept: Properties of Determinants
[4]14

Differentiate the following function with respect to x: (log x)^x+x^(logx)

Chapter: [3.01] Continuity and Differentiability
Concept: Logarithmic Differentiation
[4]15

If y=log[x+sqrt(x^2+a^2)]  show that (x^2+a^2)(d^2y)/(dx^2)+xdy/dx=0

Chapter: [3.01] Continuity and Differentiability
Concept: Logarithmic Differentiation
[4]16 | Attempt any one of the following
[4]16.1

Show that the function f(x)=|x-3|,x in R is continuous but not differentiable at x = 3.

Chapter: [3.01] Continuity and Differentiability
Concept: Concept of Continuity
[4]16.2

If x = a sin t and y = a (cost+logtan(t/2)) ,find ((d^2y)/(dx^2))

Chapter: [3.01] Continuity and Differentiability
Concept: Second Order Derivative
[4]17 | Attempt any one of the following
[4]17.1

Evaluate : intsin(x-a)/sin(x+a)dx

Chapter: [3.03] Integrals
Concept: Integration Using Trigonometric Identities
[4]17.2

Evaluate: int(5x-2)/(1+2x+3x^2)dx

Chapter: [3.03] Integrals
Concept: Integrals of Some Particular Functions
[4]18

Evaluate :  int x^2/((x^2+4)(x^2+9))dx

Chapter: [3.03] Integrals
Concept: Integrals of Some Particular Functions
[4]19

Evaluate : int_0^4(|x|+|x-2|+|x-4|)dx

Chapter: [3.03] Integrals
Concept: Evaluation of Definite Integrals by Substitution
[4]20

If veca and vecb are two vectors such that |veca+vecb|=|veca|, then prove that vector 2veca+vecb is perpendicular to vector vecb

Chapter: [4.01] Vectors
Concept: Product of Two Vectors - Scalar (Or Dot) Product of Two Vectors
[4]21 | Attempt any one of the following
[4]21.1

Find the coordinates of the point, where the line (x-2)/3=(y+1)/4=(z-2)/2 intersects the plane x − y + z − 5 = 0. Also find the angle between the line and the plane.

Chapter: [4.02] Three - Dimensional Geometry
Concept: Angle Between Line and a Plane
[4]21.2

Find the vector equation of the plane which contains the line of intersection of the planes vecr (hati+2hatj+3hatk)-4=0 and vec r (2hati+hatj-hatk)+5=0 which is perpendicular to the plane.vecr(5hati+3hatj-6hatk)+8=0

Chapter: [4.02] Three - Dimensional Geometry
Concept: Vector and Cartesian Equation of a Plane
[4]22

A speaks truth in 60% of the cases, while B in 90% of the cases. In what percent of cases are they likely to contradict each other in stating the same fact? In the cases of contradiction do you think, the statement of B will carry more weight as he speaks truth in more number of cases than A?

Chapter: [6.01] Probability
Concept: Independent Events
[6]23

A school wants to award its students for the values of Honesty, Regularity and Hard work with a total cash award of Rs 6,000. Three times the award money for Hard work added to that given for honesty amounts to Rs 11,000. The award money given for Honesty and Hard work together is double the one given for Regularity. Represent the above situation algebraically and find the award money for each value, using matrix method. Apart from these values, namely, Honesty, Regularity and Hard work, suggest one more value which the school must include for awards.

Chapter: [2.01] Matrices
Concept: Invertible Matrices
[6]24 | Attempt any one of the following
[6]24.1

Show that the height of the cylinder of maximum volume, which can be inscribed in a sphere of radius R is (2R)/sqrt3.  Also find the maximum volume.

Chapter: [3.02] Applications of Derivatives
Concept: Maxima and Minima
[6]24.2

Find the equation of the normal at a point on the curve x2 = 4y which passes through the point (1, 2). Also find the equation of the corresponding tangent.

Chapter: [3.02] Applications of Derivatives
Concept: Tangents and Normals
[6]25 | Attempt any one of the following
[6]25.1

Using integration, find the area bounded by the curve x2 = 4y and the line x = 4y − 2.

Chapter: [3.04] Applications of the Integrals
Concept: Area of the Region Bounded by a Curve and a Line
[6]25.2

Find the equation of the normal at a point on the curve x2 = 4y which passes through the point (1, 2). Also find the equation of the corresponding tangent.

Chapter: [3.02] Applications of Derivatives
Concept: Tangents and Normals
[6]26

Show that the differential equation 2yx/y dx + (y − 2x ex/y) dy = 0 is homogeneous. Find the particular solution of this differential equation, given that x = 0 when y = 1.

Chapter: [3.05] Differential Equations
Concept: Methods of Solving First Order, First Degree Differential Equations - Homogeneous Differential Equations
[6]27

Find the vector equation of the plane passing through three points with position vectors  hati+hatj-2hatk , 2hati-hatj+hatk and hati+2hatj+hatk . Also find the coordinates of the point of intersection of this plane and the line vecr=3hati-hatj-hatk lambda +(2hati-2hatj+hatk)

Chapter: [4.02] Three - Dimensional Geometry
Concept: Vector and Cartesian Equation of a Plane
[6]28

A cooperative society of farmers has 50 hectares of land to grow two crops A and B. The profits from crops A and B per hectare are estimated as Rs 10,500 and Rs 9,000 respectively. To control weeds, a liquid herbicide has to be used for crops A and B at the rate of 20 litres and 10 litres per hectare, respectively. Further not more than 800 litres of herbicide should be used in order to protect fish and wildlife using a pond which collects drainage from this land. Keeping in mind that the protection of fish and other wildlife is more important than earning profit, how much land should be allocated to each crop so as to maximize the total profit? Form an LPP from the above and solve it graphically. Do you agree with the message that the protection of wildlife is utmost necessary to preserve the balance in environment?

Chapter: [5.01] Linear Programming
Concept: Graphical Method of Solving Linear Programming Problems
[6]29

Assume that the chances of a patient having a heart attack is 40%. Assuming that a meditation and yoga course reduces the risk of heart attack by 30% and prescription of certain drug reduces its chance by 25%. At a time a patient can choose any one of the two options with equal probabilities. It is given that after going through one of the two options, the patient selected at random suffers a heart attack. Find the probability that the patient followed a course of meditation and yoga. Interpret the result and state which of the above stated methods is more beneficial for the patient.

Chapter: [6.01] Probability
Concept: Conditional Probability
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