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Math Help - find/make C subject

  1. #1
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    find/make C subject

    a= 3
    b= 2
    d= 5

    a=4b + (6/ c-1)- 15d

    okey so il show how far i am. could someone please tell me where im goin wrong. many thanks

    3= (8) + (6/ C-1) - 75
    75+3 = 8+ (6/ C-1)
    78 = 8 + (6/ C-1)
    78-8 = (6/C-1)
    70 = (6/C-1)
    C-1 (70) = 6
    C (70) = 7
    C= (7/70)
    C= 0.1
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  2. #2
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    You're right until the fourth line up from the bottom. If (c-1) definitely has brackets round then 6=70(c-1) you need to multiply out to get 6=70c-70 then rearrange. You should get c=76/70 = 1.1 approx
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  3. #3
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    but if i then subsitute 1.1 value for C then the answer should equal a= (3)?
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  4. #4
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    don't sub in 1.1 (the answer is really 1.0857....) as this is the rounded up answer. if you put c=76/70 into the original equation then you will get a=3.
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  5. #5
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    Quote Originally Posted by decoy808 View Post
    a=4b + (6/ c-1)- 15d
    You were told by Willow T that your bracketing is faulty; should be:
    a = 4b + 6 / (c-1) - 15d
    Now re-arrange:
    6 / (c-1) = a - 4b + 15d
    c - 1 = 6 / (a - 4b + 15d)
    c = 6 / (a - 4b + 15d) + 1
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  6. #6
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    Analysis

    Hi ineed to solve this exercise. Who can help me?

    Let A subset of R (real numbers) A no empty. A is annotated if and only if exist M (positive rel) such that absolute value of x is less than or equal that M, for all x in A
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