xDdraig
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Report Thread starter 4 weeks ago
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1. Deduce the smallest positive solution to the equation
10 cos2 (x – 25) = 9

The mark scheme says "x has smallest positive value when
x – 25° = –18.4°, therefore x = 6.6°". However, I go up to x-25 = cos^-1 (3 root 10 / 10). This came out as x-25 = 18.43. Thus, x = 43.43. I don't understand what I did wrong.
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DFranklin
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Cos(-18.4) = cos(18.4); picking the -18.4 solution gives you a smaller +ve value for X so is the correct choice here.
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