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Mark Thornber

@drmthornber.bsky.social

Retired A level maths teacher, current examiner. Enjoy maths puzzles and cryptic crosswords.

79 Followers  |  69 Following  |  40 Posts  |  Joined: 14.08.2024  |  2.4325

Latest posts by drmthornber.bsky.social on Bluesky

β€œSing epsilon delta, Stewart and Tall” (Google it!)

22.06.2025 18:39 β€” πŸ‘ 2    πŸ” 0    πŸ’¬ 0    πŸ“Œ 0

Graham Cumming posted a long thread on X today, with his best guesses as to what went wrong and why things turned out as badly as they did. I suspect he is right on all counts!

20.06.2025 20:21 β€” πŸ‘ 3    πŸ” 0    πŸ’¬ 4    πŸ“Œ 0

#FridayFive
1. Long Hot Summer - Tom Robinson Band
2. I Am A Town - Mary Chapin Carpenter
3. Here Comes the Sun - The Beatles
4. If You Can’t Stand The Heat - Bucks Fizz
5. Summer Breeze - The Isley Brothers

20.06.2025 20:05 β€” πŸ‘ 3    πŸ” 1    πŸ’¬ 0    πŸ“Œ 0

OCR follows Rudin etc.
Item 8.01c on the specification states:
β€˜β€œDivergence” can refer to sequences that are bounded or unbounded.’

20.06.2025 19:01 β€” πŸ‘ 1    πŸ” 0    πŸ’¬ 0    πŸ“Œ 0

I don’t think this is correct. Here is professor Peter Coles (a Newcastle lad) with the original Latin and the translations.
https://telescoper.blog/2019/11/13/newtons-laws-in-translation/

17.06.2025 17:45 β€” πŸ‘ 0    πŸ” 0    πŸ’¬ 0    πŸ“Œ 0

This list worked for me
https://bhi.co.uk/repairer/

15.06.2025 16:09 β€” πŸ‘ 0    πŸ” 0    πŸ’¬ 1    πŸ“Œ 0

Are cointerior angles really equal?

06.06.2025 22:22 β€” πŸ‘ 0    πŸ” 0    πŸ’¬ 2    πŸ“Œ 0
Post image

Out Now: 'A Tribute to Nick Lord' celebrating his work within the Mathematical Gazette and his contributions to the MA. Printed copies from Β£7, with the eBook free to MA members, or for just Β£1 to non-members.

Printed: members.m-a.org.uk/Shop/product...
eBook: members.m-a.org.uk/Shop/product...

07.05.2025 11:02 β€” πŸ‘ 4    πŸ” 1    πŸ’¬ 0    πŸ“Œ 0

For polynomials, tangent lines can be found by looking for repeated roots. No need for limits.
We find m so that p(x)-p(a)=m(x-a) has a repeated root.
This gives m=p’(a)
For quadratics it’s good old b^2-4ac=0

03.05.2025 18:19 β€” πŸ‘ 1    πŸ” 0    πŸ’¬ 1    πŸ“Œ 0

It’s definitely a US thing. Just check any of their doorstep-sized textbooks.
I always thought it was easier to remember than concave/convex, but confusion arises later when convex is used to mean β€œthe curve is under the chord”

27.02.2025 17:31 β€” πŸ‘ 1    πŸ” 0    πŸ’¬ 0    πŸ“Œ 0
Post image 23.02.2025 18:53 β€” πŸ‘ 0    πŸ” 0    πŸ’¬ 1    πŸ“Œ 0

There are a number of similar triangles. The ratios of corresponding lengths will be equal.

19.02.2025 20:28 β€” πŸ‘ 2    πŸ” 0    πŸ’¬ 1    πŸ“Œ 0

See my previous reply.

16.02.2025 09:00 β€” πŸ‘ 0    πŸ” 0    πŸ’¬ 0    πŸ“Œ 0

Lists are arrays. You can access individual items with indexing. For example L1[2]

13.02.2025 23:48 β€” πŸ‘ 0    πŸ” 0    πŸ’¬ 0    πŸ“Œ 0

I usually buy direct from the Double Two website. Lots of colours available
https://www.doubletwo.co.uk/mauve-long-sleeve-non-iron-cotton-rich-shirt/

26.01.2025 19:08 β€” πŸ‘ 1    πŸ” 0    πŸ’¬ 0    πŸ“Œ 0

The first 3 terms are (z-3)^2+1. Try the substitution u=z-3, followed by completing the square.

26.01.2025 14:02 β€” πŸ‘ 2    πŸ” 0    πŸ’¬ 1    πŸ“Œ 0
Quick cryptic | The Guardian Latest news, sport, business, comment, analysis and reviews from the Guardian, the world's leading liberal voice

You should try the Guardian quick cryptic. Each one uses 4 different clue types and they give examples of each.

https://www.theguardian.com/crosswords/series/quick-cryptic

11.01.2025 18:12 β€” πŸ‘ 1    πŸ” 0    πŸ’¬ 0    πŸ“Œ 0

There’s a typo in 2a) …

07.01.2025 19:12 β€” πŸ‘ 0    πŸ” 0    πŸ’¬ 1    πŸ“Œ 0

#FridayFive
1. On the Dark Side - Eddy and the Cruisers
2. Power In The Darkness - Tom Robinson Band
3. Because the Night - Patti Smith
4. Corcovado (Quiet Nights of Quiet Stars) - Getz, Gilberto
5. Dancing In The Dark - Cannonball Adderley

20.12.2024 22:56 β€” πŸ‘ 0    πŸ” 0    πŸ’¬ 0    πŸ“Œ 0

We have seen issues with this in the past. Some courses at some universities want to make offers on 3 A levels taken at the same time. Medicine has been a problem here.

19.12.2024 20:50 β€” πŸ‘ 1    πŸ” 0    πŸ’¬ 0    πŸ“Œ 0

I do this in Excel
1) create a scatter graph with a single point
2) use series properties to make the point invisible
3) use axis properties to get scales and labels correct
4) use major and minor grid line properties to get the grid lines looking nice
You can export to Word

19.12.2024 20:47 β€” πŸ‘ 2    πŸ” 0    πŸ’¬ 1    πŸ“Œ 0

#FridayFive
1. The Only Living Boy in New York - Simon and Garfunkel
2. My Friend Stan - Slade
3. Whatever Happened To You - Highly Likely
4. There’s a Light Beyond These Woods (Mary Margaret) - Nanci Griffith
5. Woody and Dutch on the Slow Train to Peking - Rickie Lee Jones

14.12.2024 00:41 β€” πŸ‘ 0    πŸ” 0    πŸ’¬ 0    πŸ“Œ 0

The contract had a penalty clause of Β£12000 per day for every day it ran over the agreed finish date. They finished on time!

06.12.2024 22:21 β€” πŸ‘ 3    πŸ” 0    πŸ’¬ 1    πŸ“Œ 0

When my school was rebuilt we took our FM classes to visit the site manager. He showed us a huge stack of Gantt charts for every part of the project. They tracked the number of workers used by every subcontractor every day and updated the charts every night.

06.12.2024 22:19 β€” πŸ‘ 3    πŸ” 0    πŸ’¬ 1    πŸ“Œ 0

#FridayFive
River - Joni Mitchell
Gaudete - Steeleye Span
Mary’s Boy Child - Harry Belafonte
I Believe In Father Christmas- Greg Lake
Merry Christmas Darling- The Carpenters

06.12.2024 22:03 β€” πŸ‘ 1    πŸ” 0    πŸ’¬ 0    πŸ“Œ 0

I integrate by parts

https://www.youtube.com/watch?v=-reFBJ4R9iA

27.11.2024 21:15 β€” πŸ‘ 2    πŸ” 0    πŸ’¬ 0    πŸ“Œ 0

#FridayFive
1. Winter Song - Lindisfarne
2. The Snow It Melts The Soonest - Anne Briggs
3. Mother Russia - Renaissance
4. Snowbound - Genesis
5. Under Ice - Kate Bush

22.11.2024 17:21 β€” πŸ‘ 4    πŸ” 0    πŸ’¬ 0    πŸ“Œ 0
Preview
Box plot - Wikipedia

The box and whiskers plot was first introduced in 1970, after all the hypothesis testing stuff.
en.wikipedia.org/wiki/Box_plot

15.11.2024 16:13 β€” πŸ‘ 4    πŸ” 0    πŸ’¬ 0    πŸ“Œ 0

Not needed on lines 1 or 2 because it is contained in/implied by the integral on the right.
Needed on line 3 because the LHS is indefinite, but the RHS as written is definite.

16.10.2024 18:58 β€” πŸ‘ 1    πŸ” 0    πŸ’¬ 0    πŸ“Œ 0

Simple numerical approximation:
1.4^2=1.96 so sqrt(2)>1.4
pi/4>3/4=0.75
sum>2.15>2

23.09.2024 16:38 β€” πŸ‘ 2    πŸ” 0    πŸ’¬ 1    πŸ“Œ 0

@drmthornber is following 20 prominent accounts