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# Finding max value _ maths watch

1. 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
2. (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?
3. (Original post by mikesgt2)
Max value of A is 16 isn't it?
So wats the value of a^2
4. (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
5. (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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