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katrin2010 [14]
2 years ago
12

use compound angle formulae to find sin 15 and cos 15 in form of [ surd a (surd b + c) ] . Hence, find tan 15 in the simplest su

rd form​
Mathematics
1 answer:
inysia [295]2 years ago
5 0

Answer:

see explanation

Step-by-step explanation:

Using the difference formulae for sine and cosine

sin(x - y) = sinxcosy - cosxsiny

cos(x - y) = cosxcosy + sinxsiny

sin15° = sin(45 - 30)°

sin(45 - 30)°

= sin45°cos30° - cos45°sin30°

= \frac{\sqrt{2} }{2} × \frac{\sqrt{3} }{2} - \frac{\sqrt{2} }{2} × \frac{1}{2}

= \frac{\sqrt{6} }{4} - \frac{\sqrt{2} }{4}

= \frac{\sqrt{6}-\sqrt{2}  }{4}

----------------------------------------------------------------------------------

cos15° = cos(45 - 30)°

cos(45 - 30)°

= cos45°cos30° + sin45°sin30°

= \frac{\sqrt{2} }{2} × \frac{\sqrt{3} }{2} + \frac{\sqrt{2} }{2} × \frac{1}{2}

= \frac{\sqrt{6} }{4} + \frac{\sqrt{2} }{4}

= \frac{\sqrt{6}+\sqrt{2}  }{4}

-------------------------------------------------------------------------------------

tan15° = \frac{sin15}{cos15}

= \frac{\sqrt{6}-\sqrt{2}  }{4} × \frac{4}{\sqrt{6}+\sqrt{2}  }

= \frac{\sqrt{6}-\sqrt{2}  }{\sqrt{6}+\sqrt{2}  }

Rationalise the denominator by multiplying numerator/ denominator by the conjugate of the denominator, that is (\sqrt{6} - \sqrt{2} )

= \frac{(\sqrt{6}-\sqrt{2})^2  }{(\sqrt{6}+\sqrt{2})(\sqrt{6}-\sqrt{2})    }

= \frac{6-4\sqrt{3}+2 }{6-2}

= \frac{8-4\sqrt{3} }{4}

= 2 - \sqrt{3}

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