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Anni [7]
3 years ago
15

Please explain your answer. THX!

Mathematics
1 answer:
Elden [556K]3 years ago
4 0

Answer:

see explanation

Step-by-step explanation:

(3)

Given cosΘ = - \frac{4}{5}

Then by Pythagoras' theorem the third side is 3 ( 3,4, 5 triangle )

Since Θ in second quadrant then sinΘ > 0

sinΘ = \frac{3}{5}

Using the trigonometric identity

sin2Θ = 2sinΘcosΘ, then

sin2Θ = 2 × \frac{3}{5} × - \frac{4}{5} = - \frac{24}{25}

(4)

Using the trigonometric identity

cos(x - y) = cosxcosy + sinxsiny

note cos15° = cos(45 - 30)°

cos(45 - 30) = cos45cos30 + sin45sin30

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

                    = \frac{\sqrt{2(\sqrt{3}+1) } }{4}

         

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