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- MATHEMATICS 2016 CLASS 12

General Instructions :

(i) All questions are compulsory.

(ii) This question paper contains 29 questions.

(iii) Questions 1-4 in Section A are very short-answer type questions carrying 1 mark each.

(iv) Questions 5-12 in Section B are short-answer type questions carrying 2 marks each.

(v) Questions 13-23 in Section C are long-answer I type questions carrying 4 marks each.

(vi) Questions 24-29 in Section D are long-answer II type questions carrying 6 marks each.

**SECTION – A**

Question numbers 1 to 4 carry 1 mark each.

1. If a line makes angles 90° and 60° respectively with the positive directions of x and y axes, find the angle which it makes with the positive direction of z-axis.

2.

3. If A is a 3 × 3 invertible matrix, then what will be the value of k if det(A–1) = (det A)k .

4.

**SECTION – B**

Question numbers 5 to 12 carry 2 marks each.

5. Prove that if E and F are independent events, then the events E and F’ are also independent.

6. A small firm manufactures necklaces and bracelets. The total number of necklaces and bracelets that it can handle per day is at most 24. It takes one hour to make a bracelet and half an hour to make a necklace. The maximum number of hours available per day

is 16. If the profit on a necklace is ` 100 and that on a bracelet is ` 300. Formulate on L.P.P. for finding how many of each should be produced daily to maximize the profit ? It is being given that at least one of each must be produced.

7.

8. Show that all the diagonal elements of a skew symmetric matrix are zero.

9. Find dy dx at x = 1, y = π4 if sin2y + cos xy = K.

10. Show that the function f(x) = 4x 3– 18x 2 + 27x – 7 is always increasing on .

11. Find the vector equation of the line passing through the point A(1, 2, –1) and parallel to the line 5x – 25 = 14 – 7y = 35z.

12. For the curve y = 5x – 2x 3 , if x increases at the rate of 2 units/sec, then find the rate of change of the slope of the curve when x = 3.

**SECTION – C**

Question numbers 13 to 23 carry 4 marks each.

13.

14. x2– y2 = c(x 2+ y2) Prove that x 2 – y2 = c(x 2 + y2 ) 2 is the general solution of the differential equation (x3– 3xy2)dx = (y3– 3x2y) dy, where C is a parameter.

15. Let → a = ^ i + ^ j + ^ k, → b = ^ i and → c = c1 ^ i + c2 ^ j + c3 ^ k, then (a) Let c1 = 1 and c2 = 2, find c3 which makes → a , → b and →c coplanar.

(b) If c2 = –1 and c3 = 1, show that no value of c1 can make → a , → b and →c coplanar.

16. Often it is taken that a truthful person commands, more respect in the society. A man is known to speak the truth 4 out of 5 times. He throws a die and reports that it is a six. Find the probability that it is actually a six. Do you also agree that the value of truthfulness leads to more respect in the society ?

17.

18.

19. Differentiate the function (sin x) x + sin–1 x with respect to x.

OR

If x m yn = (x + y)m + n, prove that d 2y dx 2 = 0.

20. The random variable X can take only the values 0, 1, 2, 3. Given that P(2) = P(3) = p and P(0) = 2P(1). If Σpi x 2i = 2Σpi xi , find the value of p.

21. Using vectors find the area of triangle ABC with vertices A(1, 2, 3), B(2, –1, 4) and C(4, 5, –1).

22. Solve the following L.P.P. graphically Maximise Z = 4x + y Subject to following constraints x + y ≤ 50, 3x + y ≤ 90, x ≥ 10 x, y ≥ 0.

23.

**SECTION – D**

Question numbers 24 to 29 carry 6 marks each.

24. Using integration, find the area of region bounded by the triangle whose vertices are (–2, 1), (0, 4) and (2, 3).

OR

Find the area bounded by the circle x2+ y2 = 16 and the line 3y = x in the first quadrant, using integration.

25. Solve the differential equation x dy/dx+ y = x cos x + sin x, given that y = 1 when x =π/2.

26. Find the equation of the plane through the line of intersection of →r · (2^

i – 3^ j + 4^k) = 1 and →r · (^ i – ^ j) + 4 = 0 and perpendicular to the plane →r · (2^ i – ^ j + ^ k) + 8 = 0. Hence find whether the plane thus obtained contains the line x – 1 = 2y – 4 = 3z – 12.

OR

Find the vector and Cartesian equations of a line passing through (1, 2, –4) and perpendicular to the two lines

x – 8/3 = y + 19/–16 = z – 10/ 7 and x – 15/3 = y – 29/8 = z – 5 –5.

27.

28. A metal box with a square base and vertical sides is to contain 1024 cm3 . The material for the top and bottom costs ` 5 per cm2 and the material for the sides costs ` 2.50 per cm2 . Find the least cost of the box.

29.