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If  A is an angle such that (tan A) + (sec A)=3 enter all possible values of cos A separated by commas.

 Mar 9, 2021
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Solution - 

 

\(tan A + sec A = 3 \)

\({sin A\over cos A} + {1\over cos A} = 3 \)

\(sin A + 1 = 3cos A\)

\(sin A = 3cos A - 1\)

sin2A = 9cos2A - 6cos A + 1

1 - cos2A = 9cos2A - 6cos A +1 

10cos2A - 6cos A = 0 

5cos A - 3             = 0 

cos A                    = 3/5

 Mar 9, 2021

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