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  1. #1
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    vector addition calc 3

    I'm trying to do this homework problem but I keep getting an answer that is not given. Can someone tell me what I am doing wrong please. This is for University level calc 3.

    vector addition calc 3-screen-shot-2013-09-09-7.32.18-pm.png
    so I start by naming the vectors.V is the direction the plane is now heading. V1 is the original direction of the plane. V2 is the direction of the wind.

    V = V1 + V2

    V1 = 600(cos148i+sin148j)
    V2 = 80(cos45i+sin45j)

    next I distributed, combined like terms and factored out i and j
    V = (600cos148+80cos45)i + (600sin148+80cos45)j

    I plugged that into my calculator and got
    V = <-452.7i + 374.5j>

    To find the speed I found the length of vector V
    ||V|| = sqrt[ (-452.7)2+374.52] = 587.5 km/hr

    That isn't one of the options.. am i wrong"?
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  2. #2
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    Re: vector addition calc 3

    Quote Originally Posted by shmiks View Post
    I'm trying to do this homework problem but I keep getting an answer that is not given. Can someone tell me what I am doing wrong please. This is for University level calc 3.

    Click image for larger version. 

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    so I start by naming the vectors.V is the direction the plane is now heading. V1 is the original direction of the plane. V2 is the direction of the wind.

    V = V1 + V2

    V1 = 600(cos148i+sin148j)
    V2 = 80(cos45i+sin45j)

    next I distributed, combined like terms and factored out i and j
    V = (600cos148+80cos45)i + (600sin148+80cos45)j

    I plugged that into my calculator and got
    V = <-452.7i + 374.5j>

    To find the speed I found the length of vector V
    ||V|| = sqrt[ (-452.7)2+374.52] = 587.5 km/hr

    That isn't one of the options.. am i wrong"?
    Your method is correct, but some numbers are off. I would guess that you are rounding the numbers. I usually keep all the digits when I do a calculation. I'm getting Vx = -452.260315 km/h, Vy = 397.64713 km/h, and |V| = 602.214776 km/h.

    -Dan
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  3. #3
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    Re: vector addition calc 3

    ahh you are right, I used an online calc instead of my TI-89 and got 587.2 I must have my max characters set too low or something. Thank oyu for the help
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