The known vector a + B = 2i-8j Given the vector a + B = 2i-8j, A-B = - 8i + 16J, the problem of finding a * B does not tell that I and j are unit vectors
A + B = 2i-8j = (2, - 8) -- - (1) A-B = - 8i + 16J = (- 8,16) -- (2) (1) + (2) get: 2A = (- 6,8), that is: a = (- 3,4), substituting (1) get: B = (2, - 8) - a = (2, - 8) - (- 3,4) = (5, - 12), so: a · B = (- 3,4) · (5, - 12) = - 15-48 = - 63
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