# I.S.I. B.Math Subjective Paper 2011

1. Given $$\mathbf{ a,x\in\mathbb{R}}$$ and $$\mathbf{x\geq 0,a\geq 0}$$ . Also $$\mathbf{sin(\sqrt{x+a})=sin(\sqrt{x})}$$ . What can you say about a? Justify your answer.

1. Given two cubes R and S with integer sides of lengths r and s units respectively . If the difference between volumes of the two cubes is equal to the difference in their surface areas , then prove that r=s.

1. For $$\mathbf{n\in\mathbb{N}}$$ prove that $$\mathbf{\frac{1}{2}\cdot\frac{3}{4}\cdot\frac{5}{6}\cdots\frac{2n-1}{2n}\leq\frac{1}{\sqrt{2n+1}}}$$
Solution

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1. Let $$\mathbf{t_1 < t_2 < t_3 < \cdots < t_{99}}$$ be real numbers. Consider a function $$\mathbf{f: \mathbb{R} to \mathbb{R}}$$ given by $$\mathbf{f(x)=|x-t_1|+|x-t_2|+…+|x-t_{99}|}$$ . Show that f(x) will attain minimum value at $$\mathbf{x=t_{50}}$$

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1. Consider a sequence denoted by F_n of non-square numbers . $$\mathbf{F_1=2,F_2=3,F_3=5}$$ and so on . Now , if $$\mathbf{m^2\leq F_n<(m+1)^2}$$ . Then prove that m is the integer closest to $$\mathbf{\sqrt{n}}$$

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1. Let $$\mathbf{f(x)=e^{-x} for all x\geq 0}$$ and let g be a function defined as for every integer $$\mathbf{k \ge 0}$$, a straight line joining (k,f(k)) and (k+1,f(k+1)) . Find the area between the graphs of f and g.

1. If $$\mathbf{a_1, a_2, \cdots, a_7}$$ are not necessarily distinct real numbers such that $$\mathbf{1 < a_i < 13}$$ for all i, then show that we can choose three of them such that they are the lengths of the sides of a triangle.

1. In a triangle ABC , we have a point O on BC . Now show that there exists a line l such that l||AO and l divides the triangle ABC into two halves of equal area.