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How to find the common difference of an arithmetic series? Watch

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    I'm stuck on the following practice exam question...

    The sixth term of an arithmetic sequence is twice of the third term, and the first term is 3. The sequence has 10 terms.

    I have no idea how to solve this, I tried rearranging the formula un=a+(n-1)d but did not get very far as I still cannot calculate d.

    Please help!

    Thanks.
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    U6 = 2*U3, see if you can solve it from here.

    Sent from my Nexus 7
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    Write out your formulas for each one, you know that 6th term is twice the 3rd, make them equal each other, whack a x2 in and bobs your uncle
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    (Original post by Milan945)
    I'm stuck on the following practice exam question...

    The sixth term of an arithmetic sequence is twice of the third term, and the first term is 3. The sequence has 10 terms.

    I have no idea how to solve this, I tried rearranging the formula un=a+(n-1)d but did not get very far as I still cannot calculate d.

    Please help!

    Thanks.
    u_3 = 3+2d

    u_6 = 3+5d

    u_6 = 2 u_3
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    (Original post by Mr M)
    u_3 = 3+2d

    u_6 = 3+5d

    u_6 = 2 u_3
    Hey, sorry to bother/use threads, could you possibly point me towards a guide on how to use latex? Was having a look around but couldn't find one. Much appreciated!
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    (Original post by AndroidLight)
    Hey, sorry to bother/use threads, could you possibly point me towards a guide on how to use latex? Was having a look around but couldn't find one. Much appreciated!
    http://www.thestudentroom.co.uk/wiki/LaTex
 
 
 
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