H2 Vectors (Math)

SBS1985C SG

Hi! Hope anybody could help me check my answer for this question. I think my lecturer provided the wrong ans / typo in qn. Ans Given: 1/SqROOT17

l_1 : r = ( -1,3,-3) + X (2,-1,2) l_2 : r = ( -3,1,-2) + Y (2,3,2)

Find angle between l_1 and l_2

My Working.
a.b = |a| |b| CosZ
(2,-1,2).(2,3,2) = SqROOT153 Cos Z
Cos Z = 3/SqROOT153= 1/SqROOT17 <- Could the qn been asking Find the Cosine of the angle between L_1 and L_2?

Z = 1.32 =/= 1/SqROOT17

Thanks in advance to anyone to reads or reply to this msg =)

wee_ws SG

Hi,

Angle between two lines is equivalent to angle between their direction vectors.

So cos theta = 5 / [3 sqrt(17) ].

Typo errors are common, so be sure to check with classmates.

Thanks.

Cheers,
Wen Shih