Subject

Mathematics

Class

CBSE Class 12

Pre Boards

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Sample Papers

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 Multiple Choice QuestionsLong Answer Type

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31.

Using integration, find the area of the region bounded by the triangle whose vertices are (-1, 2), (1, 5) and (3, 4).


Consider the vertices, A(-1, 2), B(1, 5) and C(3, 4).
Let us find the equation of the sides of the triangle increment ABC.
Thus, the equation of AB is:

fraction numerator straight y minus 5 over denominator 5 minus 2 end fraction space equals space fraction numerator straight x minus 1 over denominator 1 plus 1 end fraction
rightwards double arrow 3 straight x minus 2 straight y plus 7 space equals space 0
Similarly comma space the space equation space of space BC space is colon
fraction numerator straight y minus 4 over denominator 4 minus 5 end fraction equals fraction numerator straight x minus 3 over denominator 3 minus 1 end fraction
rightwards double arrow straight x plus 2 straight y minus 11 space equals 0
Also comma space the space equation space of space CA space is colon
fraction numerator straight y minus 4 over denominator 4 minus 2 end fraction space equals fraction numerator straight x minus 3 over denominator 3 plus 1 end fraction
rightwards double arrow straight x minus 2 straight y plus 5 space equals 0


Now the area of increment ABC = Area of increment ADB + Area of increment BDC

therefore space Area space of space increment ADB space equals space integral subscript negative 1 end subscript superscript 1 open square brackets fraction numerator 3 straight x plus 7 over denominator 2 end fraction minus fraction numerator straight x plus 5 over denominator 2 end fraction close square brackets dx

Similarly comma space Area space of space increment BDC equals space integral subscript 1 superscript 3 open square brackets fraction numerator 11 minus straight x over denominator 2 end fraction minus fraction numerator straight x plus 5 over denominator 2 end fraction close square brackets dx
Thus comma space Area space of space increment ADB space plus space Area space of space increment BDC
equals space integral subscript negative 1 end subscript superscript 1 open square brackets fraction numerator 3 straight x plus 7 over denominator 2 end fraction minus fraction numerator straight x plus 5 over denominator 2 end fraction close square brackets dx plus integral subscript 1 superscript 3 open square brackets fraction numerator 11 minus straight x over denominator 2 end fraction minus fraction numerator straight x plus 5 over denominator 2 end fraction close square brackets dx
equals integral subscript negative 1 end subscript superscript 1 open square brackets fraction numerator 2 straight x plus 2 over denominator 2 end fraction close square brackets dx plus integral subscript 1 superscript 3 open square brackets fraction numerator 6 minus 2 straight x over denominator 2 end fraction close square brackets dx
equals integral subscript negative 1 end subscript superscript 1 open square brackets straight x plus 1 close square brackets dx plus integral subscript 1 superscript 3 open square brackets 3 minus straight x close square brackets dx
equals open square brackets straight x squared over 2 plus straight x close square brackets subscript negative 1 end subscript superscript 1 space plus space open square brackets 3 straight x minus straight x squared over 2 close square brackets subscript 1 superscript 3
equals 0 plus 2 plus 9 minus 9 over 2 minus 3 plus 1 half
equals 2 plus 9 over 2 minus 5 over 2
equals 4 space square space units

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32.

A manufacturing company makes two types of teaching aids A and B of Mathematics for class XII. Each type of A requires 9 labour hours of fabricating and 1 labour hour for finishing. Each type of B requires 12 labour hours for fabricating and 3 labour hours for finishing. For fabricating and finishing, the maximum labour hours available per week are 180 and 30 respectively. The company makes a profit of 80 on each piece of type A and 120 on each piece of type B. How many pieces of type A and type B should be manufactured per week to get a maximum profit? Make it as an LPP and solve graphically. What is the maximum profit per week?

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33.

There are three coins. One is a two-headed coin (having head on both faces), another is a biased coin that comes up heads 75% of the times and third is also a biased coin that comes up tails 40% of the times. One of The three coins is chosen at random and tossed, and it shows heads. What is the probability that it was the two-headed coin?

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34.

Two numbers are selected at random (without replacement) from the first six positive integers. Let X denote the larger of the two numbers obtained. Find the probability distribution of the random variable X, and hence find the mean of the distribution.

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35.

Evaluate:
integral fraction numerator 1 over denominator sin to the power of 4 straight x plus sin squared xcos squared straight x plus cos to the power of 4 straight x end fraction dx

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