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    Forces P, Q and R act on a particle at the origin O, Find the magnitude of the resultatnt force and the angle it makes with ox

    a) P = 2i + 5j, Q= 3i + 4j, R = 5i + 2j
    i know to find the magnitude, you just use pythag but what about the angle?

    please help
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    Well, you have found the resultant (I hope) to be 10i + 11j. So we want to find the angle between the x-axis and 10i + 11j. Let theta be the angle between them. We have a right-angled triangle whose 'opposite' side is 11, and whose 'adjacent' side is 10. So what can we say about tan theta? Hence what is theta ?

    Hope this helps! Don't forget to draw a diagram ...
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    (Original post by Simba)
    Well, you have found the resultant (I hope) to be 10i + 11j. So we want to find the angle between the x-axis and 10i + 11j. Let theta be the angle between them. We have a right-angled triangle whose 'opposite' side is 11, and whose 'adjacent' side is 10. So what can we say about tan theta? Hence what is theta ?

    Hope this helps! Don't forget to draw a diagram ...
    argh! it looks so simple when you put it like that! thanks a lot, i'vee got it now!
 
 
 
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