Board Paper of Class 12Science 2006 Maths Delhi(SET 1)  Solutions
(i) The question paper consists of three sections A, B and C Section A is compulsory for all students. In addition to Section A, every student has to attempt either Section B OR Section C.
(ii) For Section A 
Question numbers 1 to 8 are of 3 marks each.
Question numbers 9 to 15 are of 4 marks each.
Question numbers 16 to 18 are of 6 marks each.<o:p></o:p></span></p>
(iii) For Section B/Section C
Question numbers 19 to 22 are of 3 marks each.
Question numbers 23 to 25 are of 4 marks each.
Question number 26 is of 6 marks.
(iv) All questions are compulsory.
(v) Internal choices have been provided in some questions. You have to attempt only one of the choices in such questions.
(vi) Use of calculator is not permitted. However, you may ask for logarithmic and statistical tables, if required.
 Question 1
Express the following matrix as the sum of a symmetric and a skew symmetric matrix.
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 Question 2
Using properties of determinants, prove the following:
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 Question 3
Solve the following differential equation:
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 Question 4
Form the differential equation of the family of curves y = a sin (x + b), where a and b are arbitrary constants.
Or
Solve the following differential equation:
2xy dx + (x^{2} + 2y^{2}) dy = 0
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 Question 5
Evaluate:
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 Question 6
Evaluate:
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 Question 7
Two dice are rolled once. Find the probability that:
(a) the numbers on two dice are different
(b) the total of numbers on the two dice is at least 4
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 Question 8
A pair of dice is tossed twice. If the random variable X is defined as the number of doublets, then find the probability distribution of X.
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 Question 9
 Question 10
Differentiate sin (2x+ 3) w. r. t. xfrom first principle.
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 Question 11
If, then find .
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 Question 12
 Question 13
Evaluate:
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 Question 14
Evaluate:
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 Question 15
Verify Rolle’s Theorem for the following function:
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 Question 16
Using matrices, solve the following system of equations:
x+ y+ z= 3, x −2y+ 3z= 2, and 2x − y+ z= 2
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 Question 17
Find the point on the curve y^{2}= 4x, which is nearest to the point (2, −8).
Or
Prove that the height of a right circular cylinder of maximum volume that can be inscribed in a sphere of radiusRis. Also, find the maximum volume.
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 Question 18
Find the area of the region bounded by y = 4x, x = 1, x = 4, and xaxis in the first quadrant.
Or
Evaluate as limit of a sum.
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 Question 19
If, then show that and are perpendicular to each other.
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 Question 20
Using vectors, prove that the line segment joining the midpoint of nonparallel sides of a trapezium is parallel to the base and is equal to half the sum of the parallel sides.
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 Question 21
A body moving with a velocity of 36 km/h is brought to rest in 10 seconds. Find the retardation and the distance travelled by the body before coming to rest.
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 Question 22
A particle is projected so as to graze the tops of two walls, each of height 10 m at 15 m and 45 m respectively from the point of projection. Find the angle of projection.
Or
P, Q, R, S are points in a vertical line so that P is the highest and PQ = QR = RS. If a body falls from rest at P, then prove that the times of describing the successive intervals are in the ratio
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 Question 23
ABC is a given triangle in which forces acting along OA, OB, and OC, where O is the incentre of the triangle, are in equilibrium. Prove that
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 Question 24
Two like parallel forces and act on a rigid body at A and B respectively. If and are interchanged in position, then show that the point of application of the resultant will be displaced through a distance.
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 Question 25
Find the equation of the plane passing through the points (1, 2, 3) and (0, −1, 0) and parallel to the line
Or
Find the vector and Cartesian equation of the sphere described on the join of the points (2, −3, 4) and (−5, 6, −7) as the extremities of a diameter.
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 Question 26
The vector equations of two lines are:
Find the shortest distance between the above lines.
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 Question 27
In a factory, which manufactures nuts, machines A, B, and C manufacture respectively 25%, 35%, and 40% of nuts. Of their output, 5, 4, and 2 per cent respectively are defective nuts. A nut is drawn at random from the product and is found to be defective. Find the probability that it is manufactured by machine B.
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 Question 28
If the mean and variance of the binomial distribution are respectively 9 and 6, then find the distribution.
Or
8% of people in a group are left handed. What is the probability that 2 or more of a random sample of 25 from the group are left handed? (Use e^{−2}= 0.135)
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 Question 29
What is the face value of a bill discounted at 5% per annum 73 days earlier than its legal due date, the banker’s gain being Rs 10?
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 Question 30
A bill for Rs 21,900 drawn on July 10, 2005 for 6 months was discounted for Rs 21,720 at 5% per annum. On what date was the bill discounted?
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 Question 31
A and B are partners sharing profits and losses in the ratio 3 : 4 respectively. They admit C as a new partner, the new profit sharing ratio being 2 : 2 : 3 between A, B, and C respectively. C pays Rs 12,000 as premium for goodwill. Find the amount of premium shared by A and B.
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 Question 32
Find the present worth of an ordinary annuity of Rs 1,200 per annum for 10 years at 12% per annum, compounded annually.
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[Use (1.12)^{−}^{10} = 0.3221]
 Question 33
If the total cost function is given by C = a+ bx+ cx^{2}, where xis the quantity of output, then show that:
If the marginal revenue function for a commodity is MR = 9 − 6x^{2}+ 2x, then find the total revenue function and the corresponding demand function.
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 Question 34
A dealer wishes to purchase a number of fans and sewing machines. He has only Rs 5,760 to invest and has space for at most 20 items. A fan and sewing machine cost Rs 360 and Rs 240 respectively. He can sell a fan at a profit of Rs 22 and sewing machine at a profit of Rs 18. Assuming that he can sell whatever he buys, how should he invest his money in order to maximize his profit? Translate the problem into LPP and solve it graphically.
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