What is the angle between <-8,2,8><8,2,8> and < 2,-3,5><2,3,5>?

1 Answer
Oct 19, 2016

Angle between < -8,2,8><8,2,8> and < 2,-3,5><2,3,5> is 75.28^o75.28o

Explanation:

Angle between two vectors vecu=a_1hati+b_1hatj+c_1hatku=a1ˆi+b1ˆj+c1ˆk or < a_1,b_1,c_1><a1,b1,c1>

and vecv=a_2hati+b_2hatj+c_2hatkv=a2ˆi+b2ˆj+c2ˆk or < a_2,b_2,c_2><a2,b2,c2> is given by

costheta=((vecu*vecv))/((|vecu|*|vecv|))cosθ=(uv)(uv),

where vecu*vecv=a_1a_2+b_1b_2+c_1c_2uv=a1a2+b1b2+c1c2

and |vecu|u or |vecv|v are magnitudes of vectors vecuu or vecvv and here they are

sqrt(a_1^2+b_1^2+c_1^2)a21+b21+c21 and sqrt(a_2^2+b_2^2+c_2^2)a22+b22+c22

Hence angle between < -8,2,8><8,2,8> and < 2,-3,5><2,3,5> is given by

costheta=((-8)xx2+2xx(-3)+8xx5)/(sqrt((-8)^2+2^2+8^2)xxsqrt((2)^2+(-3)^2+5^2))cosθ=(8)×2+2×(3)+8×5(8)2+22+82×(2)2+(3)2+52

= (-16-6+40)/(sqrt(64+4+64)xxsqrt(4+9+25))166+4064+4+64×4+9+25

= 18/(sqrt132xxsqrt38)18132×38

= 18/(11.4891xx6.1644)1811.4891×6.1644

= 0.254150.25415

and theta=75.28^oθ=75.28o