find the magnitude of vectors

Question

A=?+4j+4k
B=?+2j+3K
if the angle them 15 deegre

a.) by scalar product
b.) by vector product

Answer 1

Are the two ? symbols the same numerical i component, or are they different? You have one equation in each case and can only have one unknown.
If the ? components are x, the scalar product is
A*B = x^2 + 8 + 12 = x^2 + 20
and it also equals
|A||B|cos15 = sqrt(x^2+16+16)*sqrt(x^2+4+9)cos15
In principle, you could now solve for x^2, but it would be messy.
x^2 + 20 = sqrt[(x^2+32)(x^2+13)]*0.9659

Answer 2

same i