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# OCR Core 2 Jan 2008 part ii watch

1. I am writing up some solutions.
This is a Cos rule Question. We agree on part (i)

For part ii I get 0.4036 as the Cos of the Angle. The mark scheme gets 0.3998.

Here is my working

Here is their's
Section A

Where am I going wrong? Marks schemes are usually right.
2. You need to use the exact length of BD from your calculator, not the rounded value of 18.4. This then gives 0.3998 as expected.
3. (Original post by nerak99)
I am writing up some solutions.
This is a Cos rule Question. We agree on part (i)

For part ii I get 0.4036 as the Cos of the Angle. The mark scheme gets 0.3998.

Here is my working

Here is their's
Section A

Where am I going wrong? Marks schemes are usually right.
As written, the mark scheme appears to be wrong, due to rounding somewhere I guess.
4. No, it's right if you use the exact value, which is 18.44169958106291476690091790895 6. This then gives cos theta =
0.399759291404559784945513251979 7
5. (Original post by constellarknight)
No, it's right if you use the exact value, which is 18.44169958106291476690091790895 6. This then gives cos theta =
0.399759291404559784945513251979 7
Maybe, but that doesn't seem to be in the mark scheme if the OP has written it out faithfully.
6. Yes, the mark scheme is a bit confusing in that it "pretends" to use the rounded value of just 18.4, which is incorrect. Anyway hopefully nerak99 now understands the correct solution.
7. Well sometimes you just can't see for looking. Thanks

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