Problem help

[NINHARDCOREFAN]

(part 1 of 2)
Two vectors A and B, are lying in the xy
plane and given by
A = Axi +Ayj
B = Bxi +Byj
(x y are subscripts)

where A x = 4.4 m, A y = 1.74 m, B x = 7.58 m, B y = -6.76 m. Let R = A+B.
Find the magnitude of R. Answer in units
of m.

So it is
A = 4.4mI + 1.74mJ
B = 7.58mI - 5.02J

I have found out R by using the distance formula
sqrt(11.98^2 + 5.02^2) = 12.9893 m(which is right)

010 (part 2 of 2)
Find the angle that the vector R makes from
the positive x axis. Choose your answer to be
between -180 # and +180 # . The positive an_
gular direction is counter clockwise measured
from the x axis. Answer in units of # .

I tried this problem using the cosine law.
-5.02squared-11.98squared-12.99squared
______________________________________(division)
-2*11.98*12.99

I got 22.73 degrees. But when I sumbit this answer, it says I'm wrong. Can you figure out what I'm doing wrong?

[anil]

Hey is A supposed to be the distance betwen Ax and Ay [?] then here is the distance with respect origin.
A = sqrt(sqr(4.4-0)+sqr(1.74-0))
= 4.73155 = 4.7 (sig figs)

B = sqrt(sqr(7.58-0)+sqr(-6.76-0))
= 10.1564 = 10.156 (sig figs)

R = 4.7+15.26 = 15.26 -> 15.3 (sig figs)

[NINHARDCOREFAN]

I got 11.98I-5.02J by combining A and B. And the answer is right.

A=11.98 B=-5.02 C = 12.99

A
________
\ |
\ |
\ |
\ |
C \ | B
\ |
\ |
\|

I don't know which angle to find out now.

[NINHARDCOREFAN]

That was suppose to be picture of triangle
|\
A| \C
|_ \
B

[HallsofIvy]

I answered this where you posted it under "homework k-12". Please don't post the same question under different forums.

You really don't know what angle is intended? The problem said
"Find the angle that the vector R makes from the positive x axis."

Draw vector R, draw the x-axis, and STARE at it!!!