Vector Magnitude and Direction Problem

[spkenn5]

Homework Statement

Vector has a magnitude of 5.4 m and is directed east. Vector has a magnitude of 3.5 m and is directed 36° west of north. What are (a) the magnitude and (b) the direction (from east) of a + b? What are (c) the magnitude and (d) the direction (from east) of b - a ? Round your angles to the nearest degree.

The Attempt at a Solution

this is what i have attempted so far.
a) ax = 5.4m - 3.5sin36
= 3.34 m
bx = 3.5sin36
= 2.83 m
A = sqrt(3.34^2 + 2.83^2)
= 4.38 m
b) theta = arctan(2.83/3.34)
= 40.27 deg

c) ax = 5.4m + 3.5sin36
= 7.46 m
bx = 3.5sin36
= 2.83 m
A = sqrt(7.46^2 + 2.83^2)
= 7.98 m
d) STUCK.
arctan(2.83/7.46) = 20.79

I am using WileyPlus program, so they are able to detect if my answer is right or wrong. so far i have attempted these answers, and they accepted it EXCEPT the part D. i don't get what i did wrong.

thanks for the help

 

[rl.bhat]

If you measure the angle in clockwise direction, it should be taken as negative.

 

[spkenn5]

thanks for the reply!

i did the negative also. i input -20.79 and they won't accept it.

 

[rl.bhat]

thanks for the reply!

i did the negative also. i input -20.79 and they won't accept it.

They have asked the direction of (b - a), which lies in the second quadrant.

 

[spkenn5]

thanks dude you hit the spot right there!

appreciated it! now i can sleep well.