14.- Find the inverse of a given number.
Show number and result with multiples and submultiples prefix.
Information: https://www.medcalc.org/manual/decimal_multiples_and_submultiples_of_si_units.php
apk file in external link: http://kio4.com/appinventor/apk_archivos.htm
15.- Find the impedance and phase angle of a circuit RLC.
Information: https://www.youtube.com/watch?v=IVS-vjHdC1c
apk file in external link: http://kio4.com/appinventor/apk_archivos.htm
16.- Wheatstone bridge.
a) Create a random value for Rx.
b) Move the Slider until the volts are approximately zero.
c) Now Rx = R * (R2 / R1)
Information: https://www.youtube.com/watch?v=VbiOLkhQC4w
Information: https://en.wikipedia.org/wiki/Wheatstone_bridge
p82Ii_wheatstone.aia (18.4 KB) (unfinished).
apk file in external link: http://kio4.com/appinventor/apk_archivos.htm
17.- Limit of a function. Evaluate expression. Parse mathematical expressions.
To evaluate an algebraic expression we can use:
a) JavaScript: http://kio4.com/appinventor/168_javascript_evaluar_expresion.htm
b) JavaScript: https://groups.google.com/forum/#!category-topic/mitappinventortest/specific-programming-issue/0oVTthDFChY
c) Math extension by Taifun: https://puravidaapps.com/math.php
...but the proposal is to calculate the limits of these functions using only blocks.
... when approaching value is 5, we can let x = 4.99999 or 5.00001
Information: https://www.mathwarehouse.com/calculus/limits/limits-indeterminate-factorable.php
Verification: https://www.dcode.fr/limit
Examples: https://www.matesfacil.com/BAC/limites/ejercicios-resueltos-limites-1.html
p78D_limites.aia (2.4 KB)
18.- Find the prime factors of a number.
Verification: https://www.dcode.fr/prime-factors-decomposition
apk file in external link: http://kio4.com/appinventor/apk_archivos.htm
19.- Statistical.
In a class of 18 students, they have obtained the following scores:
4,4,4,5,5,5,5,5,7,7,8,8,8,8,9,9,9,10.
Calculate the mean, variance and standard deviation of that distribution.
What an excellent library of exercises! Thanks for sharing it!
20.- Minimun surface.
An open-topped cylindrical container has a volume of V = 3140 cm3. Find the cylinder dimensions (radius of base r, height v) so that the least material is needed to form the container.
From: https://www.hackmath.net/en/math-problem/5891?tag_id=91&result=1
apk file in external link: http://kio4.com/appinventor/apk_archivos.htm
On this website you can find many mathematical problems:
21.- Maximun angle.
The Statue of Liberty measures 46 m, is 47 m above ground level, look image.
What distance should one stand away from the statue in order to maximize the view of the statue? That is, what is the maximum angle Θ.
Build an application using the expressions above.
And with a Slider change value of x, get Θ and check the maximum angle Θ, in this case Θ = 19.18209º to x = 66.1 m
Information: https://www.slideshare.net/leingang/lesson-20-more-optimization-problems (pag. 20)
apk file in external link: http://kio4.com/appinventor/apk_archivos.htm
22.- Law of cosines.
In a right triangle we can calculate the c side using the Pythagorean theorem.
If the triangle is not a rectangle, we can calculate the c side using the Law of Cosines.
apk file in external link: http://kio4.com/appinventor/apk_archivos.htm
teorema_cosenos_i.aia (3.6 KB) (unfinished)
23.- Exponential regression.
Create an application to obtain the expression of an ab-exponential and e-exponential regression.
- ab-Exponential regression. 
You can get information about the ab-exponential regression in:
- e-Exponential regression. 
You can get information about the e-exponential regression in:
apk file in external link: http://kio4.com/appinventor/apk_archivos.htm
p84F2_regresion_exponencial_i.aia (30.2 KB) (unfinished)
@Juan_Antonio outstanding job with these. Please continue to share. AI2 community is very lucky to have you contributing work of your quality. God bless 
Hi, with this apk is possible calculate a integral of a real number? for example int(0,74)? tks
This is an integral
24.- Calculate PI.
Create an app to calculate the value of PI with many decimals.
The output should be a decimal sequence beginning 3.14159265 ...
25.- Find the division between two numbers by repeatedly subtracting the dividend minus the divisor.
Example: 22 / 4
hello, great demonstration !!!
if I take your first example on calculating the area of a polygon, is it possible to color it?
what is the method (I am not as efficient as you in this field, I would even say beginner :-))
Thanks for reading
perhaps see here:
