perhaps see here:
A post worth bookmarking, not just for App Inventor but also if you need help with Maths 
1 Like
26.- Cistercian Numerals.
Write a decimal number from 1 to 9999 and convert it into a Cistercian number.
Cistercian number: http://www.davidaking.org/Ciphers.htm
p91G_cisterciensesi.aia (19.3 KB)
[not finished. It contains the 36 images of the symbols, with a transparent background.]
2 Likes
Did you watch this? 
7 Likes
27.- Find the crossing point of two lines perpendicular to two sides of an equilateral triangle.
apk file in external link: http://kio4.com/appinventor/apk_archivos.htm
We have an equilateral triangle whose sides are 100.
On the left side we draw a segment of 65 and on the right side another of 47.
Find the equation of the line that passes through these points and is perpendicular to the sides.
Find the point where these lines intersect.
3 Likes
This triangle is used in various problem domains, from describing earth samples based on their proportions of sand, clay, and silt (a recent question on this forum) to choosing newly created character attribute values in the game Fallout 4 (according to my son (I haven't reached that game yet.))
The equilateral triangle has the interesting property that any point within the triangle's closest distances to the the three sides always add up to the same number, the height of the triangle.
Unfortunately, no source code is here, so we have to derive the equations from scratch.
2 Likes
28.- Mathematical proposal for Pi day.
A circle has radius 7. We draw a radius at 30º and another at 31º, as the schematic figure indicates.
a) Find the value of the segment s.
b) What is the sum of the 360 segments s drawn on the circle?
c) What value do we obtain by dividing the previous sum by the diameter of the circle?
d) Carry out the previous sections when the radius are 0.1º apart.
3 Likes
29.- Abacus Clock.
This "Abacus Clock" application indicates the actual time: HHMMSS.
It is a good idea to do it with App Inventor.
https://apkpure.com/clock-abacus/appinventor.ai_mydigitaldesk.clock_abacus
1 Like
30.- Validate Credit Card.
Write an application where the user enters a credit card number and shows if that card is valid or not.
Use the Luhn algorithm:
http://www.brainjar.com/js/validation/default2.asp
3 Likes
Can you please tell where can I download extension?
Thank you @Juan_Antonio
I tried to find in your website before I posted. But could not find the extension!.
Thanks for your help.
31.- Optical. Calculation of the scale of an image (beta).
-
On this page we can find information about the calculation of lenses:
https://www.ukessays.com/essays/physics/determination-focal-length-convex-lens-5760.php -
Here an application from the Play Store to perform physics calculations:
https://play.google.com/store/apps/details?id=de.ejbguru.android.formulaApp&hl=es&gl=US
Build an app where you enter the height of the image (G), the distance between the image and the axis of the lens (gw) and the focal length of the lens (f), and obtain the height of the projected image (B ) and the image scale (beta = B / G)
Simulator online (move Focus').
2 Likes
Thank you so much I needed this for my physics practice.
32.- Encode and decode a string using Base 45.
...Base-64 should be a well-known format, and often used to convert binary data into a text format. In Bitcoin, we use Base-58 for the Bitcoin address. But, what is Base-45?
https://billatnapier.medium.com/so-what-is-base-45-and-where-is-it-used-1ab53279d705
https://datatracker.ietf.org/doc/html/draft-faltstrom-base45-03
2 Likes
33.- When we write a number from 0 to 100, in the Textbox, the needle must mark that value in the Gauge.
- You must find the equation of the line that converts the values 0 and 100 to 315 and -315.
p91B_gauge.aia (169.8 KB) (unfinished)
1 Like
34.- Swap two numbers without using a third variable.
Now
a = 9.85
b = 2.22
After
a = 2.22
b = 9.85
p87Ci_variables.aia (2.3 KB) (unfinished)
2 Likes
35.- Draw a cycloid curve.
Ecuations:
x = r (t - sin t)
y = r (1 - cos t)
t in radians.
-
Cycloid: Cycloid - Wikipedia
-
A Cycloid is a Tautochrone curve: Tautochrone curve - Wikipedia
( is the curve for which the time taken by an object sliding without friction in uniform gravity to its lowest point is independent of its starting point on the curve.) -
Build a Tautochrone Track:
Tautochrone Track - YouTube
2 Likes