This trig-ger any memories?

You might need these:

Calculate y.

Give your answer correct to one decimal place.

Right-angled isosceles triangle with a 42° base angle and a base of 12cm


We know the hypotenuse and are trying to find the value of y, which is the adjacent.

From SOH CAH TOA, we see that we need to use the cosine ration.

\cos (x^\circ ) = \frac{{adjacent}}{{hypotenuse}}

In this case we have \cos (42^\circ ) = \frac{y}{{12}}

Rearrange using ‘change side, change operation’. We need to move the ’12’ over to the other side of the equals sign so that we have ‘y’ on its own. The ’12’ is dividing on the right hand side, so when it moves to the other side it does the opposite, therefore it will multiply.

12 \times \cos (42^\circ ) = y

y = 8.917...

y = 8.9cm\,(to\,1\,d.p.)

Remember to show all working, especially when you use a calculator.

[H/T Chuckles]

7 comments for “This trig-ger any memories?

  1. May 20, 2019 at 19:59

    Too difficult for everyone this time?

  2. Old Peculier
    May 20, 2019 at 20:59

    Sorry, the compacted sawdust between my ears spontaneously combusted 😉
    I never did get the hand of trickiernomety.

    Now i need a lie down in a dark room with a pint of my namesake,cheers 😀

  3. May 20, 2019 at 21:08

    I aced Trig in high school, but don’t remember a thing.

    “Use it or lose it,” as they say.

  4. May 20, 2019 at 22:41

    Trig – angst producer par excellence.

  5. dearieme
    May 21, 2019 at 00:01

    Good grief, that answer! What the devil is “SOH CAH TOA”?

    And why does it take three sentences to say “cross-multiply” or “multiply both sides by 12”?

    How could bright pupils possibly put up with being taught like this? So lugubriously sloooooooow.

    • May 21, 2019 at 05:08

      It’s from the current GCSE guide. Modern, young man, modern. 🙂

  6. May 21, 2019 at 05:20

    I am really quite pleased that there are mathematically inclined folk around to do all that stuff for me. Be assured though that there are other things that I can do quite well.

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