Hi and welcome to another catch the error
exercise.
I'll make a calculation and you have to be
on the lookout for the mistake.
Suppose I know that the sine of 127 (degrees)
equals about 0.8,
but I would like to know the cosine instead.
Of course I could use my calculator to directly
calculate cos(127),
but unfortunately I left it at home.
But recall there is an equation relating cosine
and sine at the same angle,
so we can use that equation instead.
This relation is sin(x)^2 + cos(x)^2 = 1,
which is just the Pythagoras theorem.
So applying it here we find that cos(127)^2 equals 1 minus sin(127)^2.
So we fill this in, and we find
that cos(127)^2 is equal to (about) 0.36.
so, we take the square root,
And now we know that cos(127) is about 0.6.
I was very happy with this result but then
later on,
I checked on my calculator,
and this answer turned out to be wrong.
Can you determine the correct answer and see
where I went wrong?
