May 9, 2014 · Also, it is quite difficult to produce the formulas for, per say, $\cos(10x)$ because as you proceed to do so, you will notice that it requires knowledge of $\cos(8x),\cos(6x),\cos(4x),\dots$, which you can eventually solve, starting with $\cos(2x)$ (it comes out to be the well known double angle formula), using this to find, $\cos(4x)$, use ...

Jul 29, 2015 · I think Augustin was answering a much more general question. In two dimensions, where we have "cosine" already defined, from trigonometry, one can show that the "dot product", defined in some other way, is equal to the lengths of the …

cos(A+B)=cosAcosB-sinAsinB. from the formula: cos(A-B)=cosAcosB+sinAsinB? The only difference that I noticed is the negative and positive sign. I was thinking that first, I replace B with (-B), but then after that how does cos(-B) turn to cos(B), and sin(-B) turn to -sin(B)? Thank you, can someone please explain to me.

May 18, 2021 · Stack Exchange Network. Stack Exchange network consists of 183 Q&A communities including Stack Overflow, the largest, most trusted online community for developers to learn, share their knowledge, and build their careers.

Apr 1, 2022 · The product $\cos A \cos B$ changes when the plane rotates The product $\sin A \sin B$ changes when the plane rotates But their sum $\cos A \cos B + \sin A \sin B $ doesn't change!

Dec 9, 2022 · Here is another way to solve for $\cos(C)$, by area calculations, done in 2 ways.. From Bob Dobb' answer, we have:

Oct 9, 2019 · Stack Exchange Network. Stack Exchange network consists of 183 Q&A communities including Stack Overflow, the largest, most trusted online community for developers to learn, share their knowledge, and build their careers.

$$\cos (A + B)\cos (A - B) = {\cos ^2}A - {\sin ^2}B$$ I have attempted this question by expanding the left side using the cosine sum and difference formulas and then multiplying, and then simplif...

Dec 5, 2020 · Why sin(A-B) is same as sin[A+(-B)]? i mean,we have derived the formula of sin(a+b) geometrically in a uniqe way..then how can we replace +b with -b in identity?

When we do vector products, we use two different methods. One is the vector dot product, another is vector cross product. The equation of the vector dot product is $$\\textbf A \\cdot \\textbf B =|\\te...