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September 4, 2015
Posted by **jack ** on Tuesday, June 18, 2013 at 2:42pm.

- maths -
**Steve**, Tuesday, June 18, 2013 at 3:38pmI assume you mean

cot^2 A(1 - 3 sec A + 2 sec^2 A)=1

If so, then

1 - 3 sec A + 2 sec^2 A = tan^2 A

sec^2 A - 3sec A + 2

(secA-1)(secA-2) = 0

secA=1 so A=0

secA=2 so A=π/3 or 5π/3

Looks like 5π/3 is the only solution > π/2

Check:

cot^2 5π/3 = 1/3

1 - 3 sec 5π/3 + 2 sec^2 5π/3 = 1-6+8 = 3