The Cosine of the angle between a and b is 4/21. Find p if a = 6i + 3j -2k and b = -2i + pj - 4k.(adsbygoogle = window.adsbygoogle || []).push({});

i started off with the general equation a . b = |a| |b| cosX where cosX is 4/21

since i, j, k all mean 1. i would get two vectors

a = (6,3,-2) and b = (-2, p, -4)

then i would take the magnitude of both a and b.

then i would take the dot product of a and b.

then i would sub them into the equation.

and then i ended up solving using the quadratic equation, but when i solved it, i ended up getting two answers and if i sub it back into the dot products and stuff it wouldn't equal.. LS = RS...

i dont kno if this is how i shouold have done it ?

thnx

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# Homework Help: Help on another algebra problem

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