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3. If θ is the angle between vector A-Axl+A, j+A.kand vector B Bi+By j+B k, then prove that:orABAyBy + A,Bcos θ =2 |
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Answer» This can be proved by dot product of A and B A•B = |A||B|cos∅ => cos∅ = A•B/(|A||B|) so, A•B = (AxBx +AyBy+AzBz) and |A| = √Ax²+Bx²+Cx² ; |B| = √Bx²+By²+Bz² => cos∅ = (AxBx+AyBy+AzBz)/√Ax²+Bx²+Cx².√Bx²+By²+Bz² |
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