If $f:\mathbb R\to\mathbb R$ and $g:\mathbb R\to\mathbb R$ are continuous functions, then evaluate
$\displaystyle \int_{-\pi/2}^{\pi/2}[f(x)+f(-x)][g(x)-g(-x)],dx$
$f(x)+f(-x)$ is an even function
$g(x)-g(-x)$ is an odd function
Product of even and odd function is odd
Integral of odd function over symmetric limits is $0$
🎓 NIMCET📅 Year: 2008📚 Mathematics🏷 Maxima and Minima
1
The maximum value of
$(\cos\alpha_1)(\cos\alpha_2)\cdots(\cos\alpha_n)$
where $0\le \alpha_1,\alpha_2,\ldots,\alpha_n\le\pi$ and
$(\cot\alpha_1)(\cot\alpha_2)\cdots(\cot\alpha_n)=1$ is
By AM–GM, maximum occurs when
$\alpha_1=\alpha_2=\cdots=\alpha_n=\frac{\pi}{4}$
Then
$\cos\alpha_i=\frac{1}{\sqrt2}$
Product $=\left(\frac{1}{\sqrt2}\right)^n=\frac{1}{2^{n/2}}$
🎓 NIMCET📅 Year: 2008📚 Mathematics🏷 Properties Of Triangle
2
Let $M$ be a point inside the triangle $ABC$. Then which one of the following is true?
A line $L$ has intercepts $a$ and $b$ on the coordinate axes. When the axes are rotated through a given angle, keeping the origin fixed, the same line has intercepts $p$ and $q$. Which of the following is true?
Intercept form of line remains invariant under rotation in terms of reciprocal squares.
Answer: $\boxed{\dfrac{1}{a^2}+\dfrac{1}{b^2}=\dfrac{1}{p^2}+\dfrac{1}{q^2}}$
Terms pair as
$f\left(\frac{k}{2001}\right)+f\left(1-\frac{k}{2001}\right)=2$
There are $1000$ such pairs.
Sum $=1000\times2=2000$
Answer: $\boxed{2000}$
🎓 NIMCET📅 Year: 2008📚 Mathematics🏷 Progressions
2
Suppose $a,b,c$ are in A.P. with common difference $d$. Then $e^{1/c},e^{1/b},e^{1/a}$ are
Coefficient of $x^{19}$ equals sum of constants:
$1+4+9+\cdots+400$
This is sum of squares from $1^2$ to $20^2$:
$\frac{20(21)(41)}{6}=2870$
Answer: $\boxed{2870}$
🎓 NIMCET📅 Year: 2008📚 Mathematics🏷 Logarithms and Indices
2
The value of
$y=0.36\log_{0.25}\left(\dfrac13+\dfrac1{3^2}+\cdots\right)$
is
The series is a G.P. with first term $\dfrac13$ and ratio $\dfrac13$.
Sum $=\dfrac{\frac13}{1-\frac13}=\dfrac12$
So
$y=0.36\log_{0.25}\left(\dfrac12\right)$
$\log_{0.25}\left(\dfrac12\right)=\dfrac{\log(1/2)}{\log(1/4)}=\dfrac{-1}{-2}=\dfrac12$
Hence
$y=0.36\times\dfrac12=0.18$
Answer: $\boxed{0.18}$