Question

Given that 0.4i+0.8j+bk is unit vector what is yhe value of b

Answer 1

Since it is a unit vector, it's magnitude = 1.
i.e.,
$\sqrt{ {0.4}^{2} + {0.8}^{2} + {b}^{2} } = 1 \\ {0.4}^{2} + {0.8}^{2} + {b}^{2} = 1\\ 0.8 + {b}^{2} = 1 \\ {b}^{2} = 1 - 0.8 = 0.2 \\ b = \sqrt{0.2} = 0.447$