# 12th Maths Paper Solutions Set 1 : CBSE All India Previous Year 2013

General Instructions:
i. All questions are compulsory.
ii. The question paper consists of 29 questions divided into three sections A, B and C. Section A comprises of 10 questions of one mark each, Section B comprises of 12 questions of four marks each, and Section C comprises of 7 questions of six marks each.
iii. All questions in section A are to be answered in one word, one sentence or as per the exact requirements of the question.
iv. There is no overall choice. However, internal choice has been provided in 4 questions of four marks each and 2 questions of six marks each. You have to attempt only one of the alternatives in all such questions.
v. Use of calculators is not permitted.
Q1 :

Write the principal value of.

Let and

and

The range of tan-1x and cot -1x is and (0,π) respectively.

and =

Therefore,

Q2 :

Write the value of.

Q3 :

For what value of x, is the matrix a skew-symmetric matrix?

If the matrix A is skew symmetric, then aij = − aji.

Therefore, x = a31 = a13 = − (−2) = 2.

Q4 :

If matrix and A2 = kA, then write the value of k.

Q5 :

Write the differential equation representing the family of curves y = mx, where m is an arbitrary constant.

Q6 :

If Aij is the cofactor of the element aij of the determinant, then write the value of a32 Â· A32.

Q7 :

P and Q are two points with position vectors respectively. Write the position vector of a point R which divides the line segment PQ in the ratio 2 : 1 externally.

Q8 :

Find, if for a unit vector .

Q9 :

Find the length of the perpendicular drawn from the origin to the plane 2x − 3y + 6z + 21 = 0.

Q10 :

The money to be spent for the welfare of the employees of a firm is proportional to the rate of change of its total revenue (marginal revenue). If the total revenue (in rupees) received from the sale of x units of a product is given by R(x) = 3x2 + 36x + 5, find the marginal revenue, when x = 5, and write which value does the question indicate.

Q11 :

Consider f : R+â†’ [4, âˆž) given by f(x) = x2 + 4. Show that f is invertible with the inverse f-1 of f given by, where R+ is the set of all non-negative real numbers.

Q12 :

Show that:

OR

Solve the following equation :

Q13 :

Using properties of determinants, prove the following:

Q14 :

If yx = ey - x, prove that .

Q15 :

Differentiate the following with respect to x :

Q16 :

Find the value of k, for which

is continuous at x = 0.

OR

If x = a cos3Î¸ and y = a sin3Î¸, then find the value of at .

Q17 :

Evaluate :

OR

Evaluate :

Q18 :

Evaluate :

Q19 :

Evaluate :

Q20 :

If , then find the value of Î», so that are perpendicular vectors.

Q21 :

Show that the lines

are intersecting. Hence find their point of intersection.

OR

Find the vector equation of the plane through the points (2, 1, -1) and (-1, 3, 4) and perpendicular to the plane x - 2y + 4z = 10.

Q22 :

The probabilities of two students A and B coming to the school in time are respectively. Assuming that the events, ‘A coming in time’ and ‘B coming in time’ are independent, find the probability of only one of them coming to the school in time.

Write at least one advantage of coming to school in time.

Q23 :

Find the area of the greatest rectangle that can be inscribed in an ellipse.

OR

Find the equations of tangents to the curve 3x2 - y2 = 8, which pass through the point.

Q24 :

Find the area of the region bounded by the parabola y = x2 and y = |x|.

Q25 :

Find the particular solution of the differential equation, given that when x = 0, y = 0.

Q26 :

Find the equation of the plane passing through the line of intersection of the planes and , whose perpendicular distance from origin is unity.

OR

Find the vector equation of the line passing through the point (1, 2, 3) and parallel to the planes.

Q27 :

In a hockey match, both teams A and B scored same number of goals up to the end of the game, so to decide the winner, the referee asked both the captains to throw a die alternately and decided that the team, whose captain gets a six first, will be declared the winner. If the captain of team A was asked to start, find their respective probabilities of winning the match and state whether the decision of the referee was fair or not.

Q28 :

A manufacturer considers that men and women workers are equally efficient and so he pays them at the same rate. He has 30 and 17 units of workers (male and female) and capital respectively, which he uses to produce two types of goods A and B. To produce one unit of A, 2 workers and 3 units of capital are required while 3 workers and 1 unit of capital is required to produce one unit of B. If A and B are priced at Rs 100 and Rs 120 per unit respectively, how should he use his resources to maximise the total revenue? Form the above as an LPP and solve graphically.

Do you agree with this view of the manufacturer that men and women workers are equally efficient and so should be paid at the same rate?