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# A2 Trigonometry watch

1. I cant get the answer for ii b

i got R as 4 and alpha as 52.24

for ii b i when i did just inverse cos of 3/4 i got 41,4096

then i added 52,24 and multiplied by 2 but did not get the correct answer.

Please tell me where i have gone wrong
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3. (Original post by uzer)
I cant get the answer for ii b

i got R as 4 and alpha as 52.24

for ii b i when i did just inverse cos of 3/4 i got 41,4096

then i added 52,24 and multiplied by 2 but did not get the correct answer.

Please tell me where i have gone wrong
That's not the smallest solution. Your range for theta is greater than zero, but your range for (1/2)theta - 52.24 is greater than -52.54. So you need to find the lowest value in this range such that its cosine is 3/4, then do the adding and multiplying by 2.
4. But how if you take inverse cos of 3/4 you get 41.409 would it be - 41.409 and why
5. (Original post by uzer)
But how if you take inverse cos of 3/4 you get 41.409 would it be - 41.409 and why
Yeah it would. Firstly because cos(x) = cos(-x) which I'm assuming you've recognized to get to that; secondly because you want a value of theta greater than zero. What you are finding first is the value of (1/2)theta - 52.24 or whatever it was. If theta is greater than zero than (1/2)theta - 52.24 is greater than -52.24. So you want to find the smallest value greater than -52.24 for which the cosine is 3/4, and that value is -41.409.
6. thanks

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