The vector a module is root 3, the vector b module is 1, and the angle between a and B is 30 degrees. Find the angle between vector (a + b) and vector (a-b)

｜a+b｜^2=4+2ab=4+3=7
｜a+b｜=√7
Similarly, A-B = 1
cosθ=（a^2-b^2）/√7=2√7/7
θ=arccos2√7/7

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