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# Is it just me who found this hard??

I was recently set this question by my maths tutor and it took me ages to do :/ I'm wondering if I was just in the wrong mind set or if it really is hard... also it's kinda fun :] All it is is to prove that sin(a-b)=cos(b)sin(a)-cos(a)sin(b). Reactions?? :]

Note by Ksenia Solovieva
4 years, 3 months ago

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Um...Its shouldn't be that hard.You probably just missed something or you have figured it out by now. I'm too lazy to to type all that.. but it should look like Vishwesh's proof below or here's one from themathpages,Khan Academy. or mayb have a look at something simple and visual. Have fun. :) · 4 years, 3 months ago

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I like the visual proof.I don't get the others. :( · 4 years, 3 months ago

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Found u on facebook. Ill message u for details on the explanations. · 4 years, 3 months ago

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Ok..cool..Be glad to help out.. :) · 4 years, 3 months ago

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It can be proved easily if you allow me to use a little geometry + trigonometry for my help · 4 years, 3 months ago

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Consider the unit circle with centre at the origin. Let x be the angle $$P_4OP_1$$and y be the angle $$P_1OP_2$$. Then (x + y) is the angle $$P_4OP_2$$. Also let (– y) be the angle $$P_4OP_3$$. Therefore, $$P_1$$, $$P_2$$, $$P_3$$ and $$P_4$$ will have the coordinates $$P_1$$(cos x, sin x), $$P_2$$ [cos (x + y), sin (x + y)], $$P_3$$ [cos (– y), sin (– y)] and $$P_4$$ (1, 0).

Sorry its hard for me to type all this. I am posting a link to the image of the solution I did. · 4 years, 3 months ago

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Here is the link to the solution:

http://s20.postimg.org/rspadf73d/image.png

http://s20.postimg.org/s6qmd0r6x/image.png

Hope that helps.... :) · 4 years, 3 months ago

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