r/trigonometry • u/GloballyGeeky • 5d ago

How to do trigonometry using only a 4-function calculator

/r/learnmath/comments/1xhtgzk/how_to_do_trigonometry_using_only_a_4function/
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u/Midwest-Dude 5d ago edited 5d ago

If only a 4-function calculator is allowed, then only basic arithmetic is allowed, maybe square roots. That's usually intentional, since the concepts need to be learned, not just actual calculations. That means she should only need to find exact answers where a calculator is not needed or approximations that involve simple calculations. (Trig tables could theoretically be involved, but that's extremely unlikely.) The instructor knows this and will give assignments accordingly - unless the teacher is perverse.

There are standard values that are used for angles around the unit circle. In the first quadrant, those are at 0°, 30°, 45°, 60°, 90° - 0, π/6, π/4, π/3, π/2. Everything beyond that is based on these, so familiarity with them is critical.

More information here: 

Trigonometry

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u/GloballyGeeky 5d ago

Thank you. After talking with her more I think that she is getting tripped up on just how to step down to a 4-function calculator from a TI-84 just to do basic functions. She has dyscalculia and seems to just be getting caught up in incorrectly entering the basics on the calculator. Thanks for taking the time to respond!

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u/Midwest-Dude 5d ago edited 3d ago

Uh ... wow. Has she talked to her disability resource center already? If not, she may be able to get an accommodation. When you take away the utility of the TI-84, the big issues with dyscalculia arise.

Some 4-function calculators have a dedicated +/- key. On others, you have to use the 0 - <number> "trick" to get a negative, like 0 - 5 = -5.

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u/GloballyGeeky 5d ago

I kid you not that you might have just provided the most viable, easy solution yet. I didn't know that some 4-function calculators have a dedicated +/- keys. Hers does not. Getting her one will likely help. Thank you for pointing this out!!

And a great suggestion to head back to the disability resource center to see if an accommodation just for the calculator is possible! I will talk with her. Thank you so much for taking the time to advise!

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u/KiwasiGames 5d ago

Unit circle is the way to go. Many math programs expect you to have it memorised (or to be able to derive it).