Problems

Construct a straight line passing through a given point and tangent to a given circle.

Three segments whose lengths are equal to $a,b$ and $c$ are given. Construct a segment of length: a) $ab/c$; b) $\sqrt{ab}$.

Construct the triangle ABC by the medians $m_a,m_b$ and $m_c$.

A chord of a circle is a straight line between two points on the circumference of the circle. Is it possible to draw five chords on a circle in such a way that there is a pentagon and two quadrilaterals among the parts into which these chords divide the circle?

Abigail’s little brother Carson found a big rectangular cake in the fridge and cut a small rectangular piece out of it.

Now Abigail needs to find a way to cut the remaining cake into two pieces of equal area with only one straight cut. How could she do that? The removed piece can be of any size or orientation.

Is it possible to cut an equilateral triangle into three equal hexagons?

We say that a figure is convex if a segment connecting any two points lays fully within the figure. On the picture below the pentagon on the left is convex and the one on the right is not.

Is it possible to draw $18$ points inside a convex pentagon so that each of the ten triangles formed by its sides and diagonals contains equal amount of points?

The triangle $ABC$ is equilateral. The point $K$ is chosen on the side $AB$ and points $L$ and $M$ are on the side $BC$ in such a way that $L$ lies on the segment $BM$. We have the following properties: $KL=KM,$ $BL=2,AK=3.$ Find the length of $CM$.

• We call two figures congruent if their corresponding sides and angles are equal. Let $ABD$ an $A^{\prime }{B}^{\prime }{D}^{\prime }$ be two right-angled triangles with right angle $D$. Then if $AD=A^{\prime }{D}^{\prime }$ and $AB=A^{\prime }{B}^{\prime }$ then the triangles $ABD$ and $A^{\prime }{B}^{\prime }{D}^{\prime }$ are congruent.

• It follows from the previous statement that if two lines $AB$ and $CD$ are parallel than angles $BCD$ and $CBA$ are equal.

We prove the other two assertions from the description:

• The sum of all internal angles of a triangle is also ${180}^{\circ }$.

• In an isosceles triangle (which has two sides of equal lengths), two angles touching the third side are equal.