i need help on this question: Find the exact value of sin 67.5 , i know that 2a is 135. and the terminal angle is 45 degree. I also need help on this, Express Pie / 2 in terms of cos A.
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Originally Posted by lickman i need help on this question: Find the exact value of sin 67.5 , i know that 2a is 135. and the terminal angle is 45 degree. [snip] $\displaystyle \cos(2 \times 67.5^o) = \cos (135^o) = - \cos(45^o)$. But from the double angle formula, $\displaystyle \cos(2 \times 67.5^o) = 1 - 2 \sin^2 (67.5^o)$. Therefore ....
arent they asking for sin?? the exact value of sin 67.5, so wouldnt u use Sin(2 x 67.5) = 2(1/square Root 2) (1/square root 2)
Originally Posted by lickman arent they asking for sin?? the exact value of sin 67.5, so wouldnt u use Sin(2 x 67.5) = 2(1/square Root 2) (1/square root 2) And how is that going to give you the value of sin(67.5), pray tell? Solve $\displaystyle -\sqrt{2} = 1 - 2 \sin^2 (67.5^o)$ as I suggested.
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