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Algebra Difficulty 3.9 AMC 10/12 Find the answer

Given that f(1,1)=1f(1,1)=1, f(m,n)N+f(m,n) \in \mathbb{N}_+ where m,nN+m,n \in \mathbb{N}_+, and for any m,nN+m,n \in \mathbb{N}_+, the following conditions are satisfied:
1. f(m,n+1)=f(m,n)+2f(m, n+1) = f(m, n) + 2;
2. f(m+1,1)=2f(m,1)f(m+1, 1) = 2f(m, 1).

What is the value of f(2010,2011)f(2010, 2011)?

A: 22010+40222^{2010} + 4022
B: 22010+20102^{2010} + 2010
C: 22010+20112^{2010} + 2011
D: 22010+40202^{2010} + 4020

Multiple choice: answer with the letter of the option you want.

Solution

Because f(1,1)=1f(1, 1) = 1, we start by considering the base case for the function ff when n=1n=1 and mm is any positive integer:

For m=1m=1, we have f(1,1)=1f(1, 1) = 1.

Using the second condition, we recursively find f(m,1)f(m, 1):
f(m+1,1)=2f(m,1)=2(2f(m1,1))==2mf(1,1)=2m. f(m+1, 1) = 2f(m, 1) = 2(2f(m-1, 1)) = \cdots = 2^m \cdot f(1, 1) = 2^m.

This allows us to establish that:
f(m,1)=2m1. f(m,1)=2^{m-1}.

Now, using the first condition, we can iteratively calculate f(m,n)f(m, n) where n>1n > 1:
f(m,n+1)=f(m,n)+2. f(m, n+1) = f(m, n) + 2.

Repeatedly applying this condition starting from f(m,1)f(m, 1) for any specific mm, we get:
f(m,2)=f(m,1)+2=2m1+2,f(m,3)=f(m,2)+2=2m1+4,f(m,n)=2m1+2(n1). f(m, 2) = f(m, 1) + 2 = 2^{m-1} + 2, \\ f(m, 3) = f(m, 2) + 2 = 2^{m-1} + 4, \\ \vdots \\ f(m, n) = 2^{m-1} + 2(n-1).

Thus, in general, we can represent f(m,n)f(m, n) as:
f(m,n)=2m1+2(n1). f(m, n) = 2^{m-1} + 2(n-1).

Applying this formula to find f(2010,2011)f(2010, 2011), we obtain:
f(2010,2011)=220101+2(20111)=22009+22010. f(2010, 2011) = 2^{2010-1} + 2(2011-1) = 2^{2009} + 2 \cdot 2010.

Since 220092^{2009} is equal to 22010÷22^{2010} \div 2, we can write:
f(2010,2011)=220102+4020=22009+4020. f(2010, 2011) = \frac{2^{2010}}{2} + 4020 = 2^{2009} + 4020.

But we need this value in terms of 220102^{2010} to match the answer choices, so multiplying both terms in the sum by 2 we get:
f(2010,2011)=22010+24020=22010+4020+2 f(2010, 2011) = 2^{2010} + 2 \cdot 4020 = 2^{2010} + \boxed{ 4020 + 2 }

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Source: NuminaMath-1.5, licensed Apache-2.0. Statement and solution reproduced as published; topic and difficulty added by this site.