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# Board Paper of Class 12-Science 2015 Maths (SET 3) - Solutions

General Instructions :
(i) All questions are compulsory.
(ii) Please check that this Question Paper contains 26 Questions.
(iii) Marks for each question are indicated against it.
(iv) Questions 1 to 6 in Section-A are Very Short Answer Type Questions carrying one mark each.
(v) Questions 7 to 19 in Section-B are Long Answer I Type Questions carrying 4 marks each.
(vi) Questions 20 to 26 in Section-C are Long Answer II Type Questions carrying 6 marks each.
(vii) Please write down the serial number of the Question before attempting it.
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• Question 1
Find the differential equation representing the family of curves $\mathrm{v}=\frac{\mathrm{A}}{\mathrm{r}}$+ B, where A and B are arbitrary constants. VIEW SOLUTION
• Question 2
Find the integrating factor of the differential equation
$\left(\frac{{{e}^{-2}}^{\sqrt{x}}}{\sqrt{x}}-\frac{y}{\sqrt{x}}\right)\frac{dx}{dy}=1$. VIEW SOLUTION
• Question 5
If a line makes angles 90°, 60° and θ with x, y and z-axis respectively, where θ is acute, then find θ. VIEW SOLUTION
• Question 6
Write the element a23 of a 3 ✕ 3 matrix A = (aij) whose elements aij are given by ${a}_{ij}=\frac{\left|i-j\right|}{2}.$ VIEW SOLUTION
• Question 7
If x = a cos θ + b sin θ, y = a sin θ − b cos θ, show that ${y}^{2}\frac{{d}^{2}y}{d{x}^{2}}-x\frac{dy}{dx}+y=0.$ VIEW SOLUTION
• Question 8
The side of an equilateral triangle is increasing at the rate of 2 cm/s. At what rate is its area increasing when the side of the triangle is 20 cm ? VIEW SOLUTION
• Question 10
Three schools A, B and C organized a mela for collecting funds for helping the rehabilitation of flood victims. They sold hand made fans, mats and plates from recycled material at a cost of Rs 25, Rs 100 and Rs 50 each. The number of articles sold are given below:
 School Article A B C Hand-fans 40 25 35 Mats 50 40 50 Plates 20 30 40

Find the funds collected by each school separately by selling the above articles. Also find the total funds collected for the purpose.

Write one value generated by the above situation. VIEW SOLUTION
• Question 11
If $\mathrm{A}=\left(\begin{array}{ccc}2& 0& 1\\ 2& 1& 3\\ 1& -1& 0\end{array}\right)$ find ${\mathrm{A}}^{2}-5\mathrm{A}+4\mathrm{I}$ and hence find a matrix X such that ${\mathrm{A}}^{2}-5\mathrm{A}+4\mathrm{I}+\mathrm{X}=\mathrm{O}$

OR

If VIEW SOLUTION
• Question 12
If $f\left(x\right)=\left|\begin{array}{ccc}a& -1& 0\\ ax& a& -1\\ a{x}^{2}& ax& a\end{array}\right|$, using properties of determinants find the value of f(2x) − f(x). VIEW SOLUTION
• Question 13
Find :

OR

Integrate the following w.r.t. x
$\frac{{x}^{2}-3x+1}{\sqrt{1-{x}^{2}}}$ VIEW SOLUTION
• Question 15
A bag A contains 4 black and 6 red balls and bag B contains 7 black and 3 red balls. A die is thrown. If 1 or 2 appears on it, then bag A is chosen, otherwise bag B, If two balls are drawn at random (without replacement) from the selected bag, find the probability of one of them being red and another black.
OR
An unbiased coin is tossed 4 times. Find the mean and variance of the number of heads obtained. VIEW SOLUTION
• Question 16
• Question 17
Find the distance between the point (−1, −5, −10) and the point of intersection of the line $\frac{x-2}{3}=\frac{y+1}{4}=\frac{z-2}{12}$ and the plane xy + z = 5. VIEW SOLUTION
• Question 18
If sin [cot−1 (x+1)] = cos(tan1x), then find x.

OR

If (tan1x)2 + (cot−1x)2 = $\frac{5{\mathrm{\pi }}^{2}}{8}$, then find x. VIEW SOLUTION
• Question 19
If then find $\frac{dy}{dx}$. VIEW SOLUTION
• Question 20
If A and B are two independent events such that then find P(A) and P(B). VIEW SOLUTION
• Question 21
Find the local maxima and local minima, of the function f(x) = sin x − cos x, 0 < x < 2π. VIEW SOLUTION
• Question 22
Find graphically, the maximum value of z = 2x + 5y, subject to constraints given below :

VIEW SOLUTION
• Question 23
Let N denote the set of all natural numbers and R be the relation on N × N defined by (a, b) R (c, d) if ad (b + c) = bc (a + d). Show that R is an equivalence relation. VIEW SOLUTION
• Question 24

Using integration find the area of the triangle formed by positive x-axis and tangent and normal of the circle

OR

Evaluate as a limit of a sum.

VIEW SOLUTION
• Question 25

Solve the differential equation :

$\left({\mathrm{tan}}^{-1}y-x\right)dy=\left(1+{y}^{2}\right)dx.$

OR

Find the particular solution of the differential equation $\frac{dy}{dx}=\frac{xy}{{x}^{2}+{y}^{2}}$ given that y = 1, when x = 0. VIEW SOLUTION
• Question 26
If lines intersect, then find the value of k and hence find the equation of the plane containing these lines. VIEW SOLUTION
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