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    Hello, I have this question it says

    find the maximum value of A = 8r - r^2 by first writing as

    A = a^2 - (r - b)^2 for suitable values of a and b . At which value of r does this occur?

    I worked out b as +4 but whats a^2

    thanks
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    (Original post by Learner1)
    Hello, I have this question it says

    find the maximum value of A = 8r - r^2 by first writing as

    A = a^2 - (r - b)^2 for suitable values of a and b . At which value of r does this occur?

    I worked out b as +4 but whats a^2

    thanks
    Max value of A is 16 isn't it?
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    (Original post by mikesgt2)
    Max value of A is 16 isn't it?
    So wats the value of a^2
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    (Original post by Learner1)
    Hello, I have this question it says

    find the maximum value of A = 8r - r^2 by first writing as

    A = a^2 - (r - b)^2 for suitable values of a and b . At which value of r does this occur?

    I worked out b as +4 but whats a^2

    thanks
    You can complete the square:

    A = - [r^2 - 8r]

    A = - [(r-4)^2 - 16]

    take the "-" into the bracket to get: A = -(r-4)^2 + 16

    So, A = 16 - (r-4)^2

    A = (4)^2 - (r-4)^2

    Therefore the maximum value of A is 16 when, r = 4
    a = 4 (so a^2 = 16)
    b = 4
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    (Original post by mockel)
    You can complete the square:

    A = - [r^2 - 8r]

    A = - [(r-4)^2 - 16]

    take the "-" into the bracket to get: A = -(r-4)^2 + 16

    So, A = 16 - (r-4)^2

    A = (4)^2 - (r-4)^2

    Therefore the maximum value of A is 16 when, r = 4
    a = 4 (so a^2 = 16)
    b = 4
    Hello, i thought so, thank u for clarification
 
 
 
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