
Name: lena
Subject: trigonometry
Who is asking: Student
Level: Secondary
Question:
how do you add vectors together?
If you are given the length and angles of both vectors and are asked to add/subtract them, how do you do it? I know you are supposed to do the head to tail method, but whenever i try it i get the wrong answer. I need help setting it up.
example: A is 2.7cm, and 60 degrees, B is 1.6cm and 135 degrees, find the magnitude and amplitude
Thanks a lot!
Hi Lena,
Here is my diagram.
From the diagram and the values given, OA = 2.7 cm, OB = AC = 1.6 cm and the angle OAC has measure 105^{o}.
You can find the length of OC using the law of cosines.
OC^{2}
= OA^{2} + AC^{2}  2 OAAC cos(angle OAC)
= 2.7^{2} + 1.6^{2}  2 x 2.7 x 1.6 cos(105^{o})
Since cos(105^{o})is negative, OC^{2} is larger than 2.7^{2} + 1.6^{2}. I got OC = 3.45 cm.
To finish the problem you need to find the measure of the angle COA. This you can find using the law of sines,
^{sin(COA)}/_{AC} = ^{sin(OAC)}/_{OC}
I hope this helps,
Penny
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