Some Brain Twisters/~[part 1]

1)...... let A0 denotes the area bounded by f_{n}(x)=\left|\frac{sin(8nx)+cos(8nx)}{x} \right| , x -axis,y-axis and the line x=\pi /8

the prove that A_{n}>\frac{2\sqrt{2}}{\pi }\left[1+\frac{1}{2}.......\frac{1}{n} \right]
(n\epsilon N)
_______________________________________________________________

2).....let set S contains infinite positive elements S:\left\{\theta _{1}+\theta _{2}+\theta _{3}+........ \right\}
such tat sum of all elements is \pi

show tat sin(\theta _{1})+sin(\theta _{2})+sin(\theta _{3})+.......\leq \pi

_______________________________________________________________

3)....Let Tnn=1,2,3,4 represent four distinct positive real nos oder than unity such that each pair of the logarithm of Tn and the reciprocal of the logarithm denotes a point on a circle ,whose center lies on y axis.....find minimum value of T_{1}+T_{2}+T_{3}+T_{4}...(this one is easy)

________________________________________________________________

4).....let \vec{r} is a position vector of a variable point in cartesian OXY plane such that
\vec{r}.(10\hat{j}-8\hat{i}-\vec{r})=40 and p_{1}=max\left\{\left|\bar{r}+2\hat{i}-3\hat{j} \right|^{2} \right\}and p_{1}=min\left\{\left|\bar{r}+2\hat{i}-3\hat{j} \right|^{2} \right\}.
A tangent line is drawn to teh curve y=8/x2 at teh point A with absicca 2 if p1+p2 is even otherwise a normal line is drawn at teh same point.teh drawn line cuts the x-axis at a point B. find \bar{AB}.\bar{OB}

note a typo---(its P2=min{ })
________________________________________________________________

2 Answers

1
gordo ·

the first and second are pretty straight foward..,
for the first one,

I=I1+I2+I3...+In

whr Ik= ∫(/sinnx +cosnx/)/xdx from (k-1)pi/8 to kpi/8

Ik>∫(/sin nx +cosnx/) * (1/kpi) dx from (k-1)pi/8 to kpi/8

summation Ik =I>1/pi*[∫(/sin nx +cosnx/)dx from 0 to pi/8]*[1+1/2+1/3....1/n]

all u have to do is to evaluate the definite integral of √2sin(pi/4+x)
from 0 to pi/8

for the second one, for any x>0 x>=sinx

so ∂1>=sin∂1
∂2>=sin∂2
∂3>=sin∂3
..............
summing up, pi>=sin∂1+sin∂2+sin∂3....sin∂n

cheers!!

21
eragon24 _Retired ·

@gordo array all r pretty much straightforward......btw is 2nd one so straightforward[3].......i initially thought of lik tat....but then its a q from a mock Q paper for iit mains which used to come long back 6-7 yrs ago...how can they give a subjective q lik tat....so straightforward.[3]

and P.S des r not ma doubt.....

Your Answer

Close [X]