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simplfying help please watch

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    hi there, ive been stuck on this bit of vector product proof kind of thing for quite a while, need a bit of help thanks

    x1a1+x2a2+x3a3=0

    x1b1+x2b2+x3b3=0

    how do i eliminate x3?

    i cant seem to find a way

    btw x1 means x with a little 1, showing theres 3 different x's, same with a's and b's
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    put the x3 on its own in both cases and then equate the two different equations!
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    (Original post by chr15chr15)
    put the x3 on its own in both cases and then equate the two different equations!
    Yes!
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    To write x_3 you can use latex. See here:How to use LaTeX
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    In general, you solve simultaneous equations by eliminating the variables one at a time.

    In this case, you pick an equation with the variable you want to eliminate in it (either will do), multiply / divide by some constant so the co-efficient of that variable is 1 (in the first; divide through by a_3 giving \frac{a_1x_1}{a_3} + \frac{a_2x_2}{a_3} + x_3 = 0. Now, you subtract from to every other equation you have, some multiple of this equation, chosen so that it cancels the variable you're eliminating.
    Spoiler:
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    So for this we'd subtract b_3 lots of the (modified) first equation from the second, giving x_1(b_1-\frac{b_3a_1}{a_3}) + x_2(b_2-\frac{b_3a_2}{a_3}) = 0
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    (Original post by pyrolol)
    In general, you solve simultaneous equations by eliminating the variables one at a time.

    In this case, you pick an equation with the variable you want to eliminate in it (either will do), multiply / divide by some constant so the co-efficient of that variable is 1 (in the first; divide through by a_3 giving \frac{a_1x_1}{a_3} + \frac{a_2x_2}{a_3} + x_3 = 0. Now, you subtract from to every other equation you have, some multiple of this equation, chosen so that it cancels the variable you're eliminating.
    Spoiler:
    Show
    So for this we'd subtract b_3 lots of the (modified) first equation from the second, giving x_1(b_1-\frac{b_3a_1}{a_3}) + x_2(b_2-\frac{b_3a_2}{a_3}) = 0
    but you won't be able to solve this system of equations with only 2 equations.
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    god how did i not think of that :rolleyes: :o: cheers

    and thanks for the latex thing Simon
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    (Original post by Totally Tom)
    but you won't be able to solve this system of equations with only 2 equations.
    Course not, that first line was more a vague mention.
 
 
 
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