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uplakanimkk 2022-07-07 Answered
If b = sin ( 40 + α ) and 0 < α < 45 , compute cos ( 70 + α ) in terms of b
I wrote cos ( 70 + α ) = cos ( 30 + 40 + α ) = 3 2 cos ( 40 + α ) 1 2 b ,, this didn't work. Then expanded sin ( 40 + α ) and cos ( 70 + α ) in the hope of getting a hint. Still and all, I couldn't get the answer up above.
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Answers (1)

Allison Pena
Answered 2022-07-08 Author has 14 answers
cos ( 70 + α ) = cos ( 40 + α + 30 ) =
cos ( 40 + α ) cos ( 30 ) sin ( 40 + α ) sin ( 30 ) =
1 sin ( 40 + α ) 2 3 2 b 2
= 1 b 2 3 2 b 2

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