finding angle between vectors

[nickname]

v=<-1,1>, w=<5,12>

I did:

v dot w= v1w1+v2w2= -1x5 + 1x12= -5+12= 7

llvll llwll = square root((1^2)+(5^2)) times square root((1^2)+(12^2))= square root of 26 times square root of 145.

angle= cos^-1 (7/(square root of 26 times square root of 145)= cos^-1(0.1140)= 83.45degrees= my answer, but the correct answer is 67.6degrees.

What steps did I do wrong? Did I use the correct formula?


Thank you

 

[Aladdin]

cos(v,u)=7/sqrt2*sqrt169=7/sqrt338 , cos^-1=67.6 degrees

 

[nickname]

Thanks for replying. How did you get square root of 2 and square root of 169?

 

[Aladdin]

Thanks for replying. How did you get square root of 2 and square root of 169?

You have to get the magnitude of each vector:u=sqrt1^2+1^2
magnitude of v=sqrt5^2+12^2
I hope you understood it, because i got to go to school :wink:

 

[nickname]

Thank you so much! I was plugging the wrong value for the magnitutes.

Thanks again!