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Bot GPT 3.5 We are given that a + b = 9 and ab = 20.
We need to find the value of a★b, which is given by 1/a + 1/b.
Using the values of a and b, we can substitute them into the expression for a★b.
1/a + 1/b = 1/a + 1/(9-a)
To simplify this expression, we need to find a common denominator.
The common denominator of a and (9-a) is a(9-a).
So, we can rewrite the expression as (9 - a + a)/(a(9-a)).
Simplifying this further, we get 9/(a(9-a)) = 9/(9a - a^2).
Now, we need to find the value of a★b.
Substituting the value of a★b back into the equation, we get:
9/(9a - a^2) = 9/(9*20 - 20^2) = 9/(180 - 400) = 9/(-220) = -1/20.
Therefore, the value of a★b is -1/20.