Why Is My Calculation for the X Component of the Vector Sum Incorrect?

[STEF2098]

The two vectors a and b have equal magnitudes of 13.0 m and their angles are θ1 = 30° and θ2 = 100°.
Find the components of their vector sum, r.


I know this is a very simple problem, but I can't get it! And it is frustrating me to no end.

I know the y component of the sum is 16.3. (I don't remember how I got this, but it's right.)
However, when I try to find the x components of each vector, I get 11.26 for a, and -2.26 for b. When these are added, you get 9.0. And the computer(our HW is graded online) is telling me that this is the wrong answer.

What am I doing wrong?!

 

[tiny-tim]

The two vectors a and b have equal magnitudes of 13.0 m and their angles are θ1 = 30° and θ2 = 100°.
Find the components of their vector sum, r.
…
I know the y component of the sum is 16.3. (I don't remember how I got this, but it's right.)
However, when I try to find the x components of each vector, I get 11.26 for a, and -2.26 for b. When these are added, you get 9.0. And the computer(our HW is graded online) is telling me that this is the wrong answer.

What am I doing wrong?!

Hi STEF2098!

hmm … I make it 9.0 also, but I don't get 16.3

are you sure it's not |a| = |b| = 11.0 m?