Hi

I need help on the following questions:

1)Given $\displaystyle a=i+2j+3k, b=2i-3j+2k$ and $\displaystyle c=i+j-k$, find the angle between b and c.

This is what i have done:$\displaystyle cos^{-1}\frac{2}{\sqrt17\sqrt1}$

=60'58'

answers says its 114'50'

2)Given $\displaystyle x=2i-j+k$ and $\displaystyle y=i+j+tk$ find the value of t if the angle between the two vectors is 60 degree

P.S