Solve the congruence x^20 - 1 -= 0(mod 61)

To prove: The two triangles are similar using postulate or theorem.
Given information:
The system triangles:

Maximize
$f(x,y,z)=xy+z^2,$
while $2x-y=0$ and $x+z=0$. Lagrange doesnt seem to work.

To find: the name of the corresponding parts in the congruent triangles. And complete the congruence statement.
Given:
The congruence statement is ${\displaystyle \mathrm{△}CAB}$.

Find the area of the shaded region. Round to the nearest tenth.

Area of the shaded region=

Mathematical expectation of the average distance of some set of points
In cartesian plane, N points are randomly generated within a unit square defined by points (0,0)(0,1)(1,1)(1,0), with uniform distribution. What is the mathematical expectation of the average distance of all distances between all points (distances between the point and the same point (which are obviously 0) are excluded from the calculation of the average).
There are actually two versions of this question:
- Distance is defined as Euclidian.
- Distance is defined as Manhattan.
The context of this question is some performance benchmarking in computer science, which are of practical nature and far from pure mathemathics, so I am not going the bother the reader with these details.

Given:
${\displaystyle \mathrm{△}GRA}$
${\displaystyle \mathrm{\angle }GRA={85}^{\circ }}$
${\displaystyle \mathrm{\angle }RGA={63}^{\circ }}$
${\displaystyle \mathrm{\angle }RAG={?}^{\circ }}$

Converting between the $y=e+dx$ and $ax+by=c$ forms of a line equation