[unknown123]

Could some one please tell me where I am going wrong in answering this question

its jan 08 http://www.ocr.org.uk/download/pp_08..._jan_l_gce.pdf

basically you have to find the angle

so i use the cosine formula

cosA= c^2 + b^2 - a^2/ 2bc

a=18.4
b=20
c=10

so cosa= 100+400 - 338.56/ 400=

cosA= 0.4036

however in the mark scheme it says

cos A= 0.3998

mark scheme link: http://www.ocr.org.uk/download/ms_08..._l_gce_jan.pdf

could some one please tell me why my answer is different to the one in the mark scheme

[TenOfThem]

Because you rounded off the 18.4.............

[steve2005]

(Original post by unknown123)
Could some one please tell me where I am going wrong in answering this question

its jan 08 http://www.ocr.org.uk/download/pp_08..._jan_l_gce.pdf

basically you have to find the angle

so i use the cosine formula

cosA= c^2 + b^2 - a^2/ 2bc

a=18.4
b=20
c=10

so cosa= 100+400 - 338.56/ 400=

cosA= 0.4036

however in the mark scheme it says

cos A= 0.3998

mark scheme link: http://www.ocr.org.uk/download/ms_08..._l_gce_jan.pdf

could some one please tell me why my answer is different to the one in the mark scheme

You have rounded TOO SOON, your 338.56 is wrong It should be 340.07

I think you squared 18.4 instead of 18.441 ALWAYS use the best figure available.

[Pride]

wait, which question are you talking about?

[unknown123]

question 4)ii

I now know why it was wrong.


thanks guys

[GreenLantern1]

merked the last question