2015 Issue 461

  1. Let $(2n-1)!!$ and $(2n)!!$ donote the products $1.3.5\ldots(2n-1)$ and $2.4.6\ldots(2n)$ respectively. Prove that the number \[A=(2013)!!+(2014)!!\] is divisible by $2015.$
  2. Given an isolates triangle $ABC$ with $AB=AC$ and $\widehat{A}=3\widehat{B}$. On the half-plane determined by $BC$ that contians $A$, draw the array $Cy$ such that $\widehat{BCy}=132^{0}$. The array $Cy$ intersects the bisector $Bx$ of the angle $B$ at $D$. Calculate $\widehat{ADB}$.
  3. Solve the equation \[\frac{1}{\sqrt{x^{2}+3}}+\frac{1}{\sqrt{1+3x^{2}}}=\frac{2}{x+1}.\]
  4. Given an equilateral triangle $ABC$ and a point $)$ inside the triangle. Let $M,N,P$ respectively be the intersections between $AO,BO,CO$ and the sides of the triangle. Prove that
    a) ${\displaystyle \frac{1}{AM}+\frac{1}{BN}+\frac{1}{CP}\leq\frac{1}{3}\left(\frac{1}{OM}+\frac{1}{ON}+\frac{1}{OP}\right)}$,
    b) ${\displaystyle \frac{1}{AM}+\frac{1}{BN}+\frac{1}{CP}\leq\frac{2}{3}\left(\frac{1}{OA}+\frac{1}{OB}+\frac{1}{OC}\right)}$.
  5. Solve the system of equations \[\begin{cases} \sqrt[3]{9(x\sqrt{x}+y^{3}+z^{3})} & =x+y+z\\ x^{2}+\sqrt{y} & =2z\\ \sqrt{y}+z^{2} & =\sqrt{1-x}+2 \end{cases}.\]
  6. Solve the equation \[(x+1)(x+2)(x+3)=\frac{720}{(x+4)(x+5)(x+6)}.\]
  7. Determine the number of solutions of each following equation
    a) ${\displaystyle \sin x=\frac{x}{1964}}$,
    b) $\sin x=\log_{100}x$,
  8. Given a triangle $ABC$ inscribed in a circle $(O)$. The bisectors of the angles $A,B,C$ respectively intersects the circle at $D$, $E$, $F$. Denote respectively by $h_{a},h_{b},h_{c},S$ the heights from $A,B,C$ and the area of $ABC$. Prove that \[AD.h_{1}+BE.h_{b}+CF.h_{c}\geq4\sqrt{3}S.\]
  9. Given real numbers $a,b,c,d$ satisfying \[a^{2}+b^{2}+c^{2}+d^{2}=1.\] Find the maximum and minimum values of the expression \[P=ab+ac+ad+bc+cd+3cd.\]
  10. Given $k\geq1$ and positive numbers $x,y$. For any positive integer $n\geq2$, show the following inequalities \[\sqrt{xy}\leq\sqrt[n]{\frac{x^{n}+y^{n}+k[(x+y)^{n}-x^{n}-y^{n}]}{2+k(2^{n}-2)}}\leq\frac{x+y}{2}.\]
  11. A pair of positive integers is called a good pair if their quotient if either $2$ or $3$. What is the most number of good pairs we can get among $2015^{2016}$ arbitrary different positive integers?.
  12. Given a triangle $ABC$. Let $E,F$ respectively be the perpendicular projections of $B,C$ on $AC,AB$; and then let $T$ be the perpendicular projection of $A$ on $EF$. Denote the midpoints of $BE$ and $CF$ by $M$ and $N$ respectively. Suppose that $TM,TN$ intersects $AB,AC$ respectively at $P,Q$. Prove that $EF$ goes through the midpoint of $PQ$,




Mathematics & Youth: 2015 Issue 461
2015 Issue 461
Mathematics & Youth
Loaded All Posts Not found any posts VIEW ALL Readmore Reply Cancel reply Delete By Home PAGES POSTS View All RECOMMENDED FOR YOU LABEL ARCHIVE SEARCH ALL POSTS Not found any post match with your request Back Home Sunday Monday Tuesday Wednesday Thursday Friday Saturday Sun Mon Tue Wed Thu Fri Sat January February March April May June July August September October November December Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec just now 1 minute ago $$1$$ minutes ago 1 hour ago $$1$$ hours ago Yesterday $$1$$ days ago $$1$$ weeks ago more than 5 weeks ago Followers Follow THIS CONTENT IS PREMIUM Please share to unlock Copy All Code Select All Code All codes were copied to your clipboard Can not copy the codes / texts, please press [CTRL]+[C] (or CMD+C with Mac) to copy