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Algebra Difficulty 3.4 AMC 10/12 Find the answer

Let f(x)=msin(πx+α1)+ncos(πx+α2)f(x) = m\sin(\pi x + \alpha_1) + n\cos(\pi x + \alpha_2), where mm, nn, α1\alpha_1, and α2\alpha_2 are all non-zero real numbers. If f(2011)=1f(2011) = 1, then f(2012)=f(2012) = ______.

A number or a short expression. Fractions can be typed as 3/2, and spacing doesn't matter.

Solutions — 2

Solution 1

Since f(2011)=1f(2011) = 1, we have:
msin(2011π+α1)+ncos(2011π+α2)=1. m\sin(2011\pi + \alpha_1) + n\cos(2011\pi + \alpha_2) = 1.

Using the properties of sine and cosine concerning odd and even multiples of π\pi, we have:
sin(2011π+α1)=sin(α1) \sin(2011\pi + \alpha_1) = \sin(\alpha_1)
and
cos(2011π+α2)=cos(α2). \cos(2011\pi + \alpha_2) = -\cos(\alpha_2).
This simplification arises because 2011π2011\pi is an odd multiple of π\pi which makes sine function remain the same due to its periodicity, while cosine changes sign.

Hence, we can rewrite the equation as:
msin(α1)ncos(α2)=1, -msin(\alpha_1) - n\cos(\alpha_2) = 1,
which leads to:
msin(α1)+ncos(α2)=1 msin(\alpha_1) + n\cos(\alpha_2) = -1

Now, let's find f(2012)f(2012) using an analogous argument:
f(2012)=msin(2012π+α1)+ncos(2012π+α2). f(2012) = m\sin(2012\pi + \alpha_1) + n\cos(2012\pi + \alpha_2).

Since 2012π2012\pi is an even multiple of π\pi, both sin\sin and cos\cos functions will not change sign with respect to their respective offsets, thus we have:
sin(2012π+α1)=sin(α1) \sin(2012\pi + \alpha_1) = \sin(\alpha_1)
and
cos(2012π+α2)=cos(α2). \cos(2012\pi + \alpha_2) = \cos(\alpha_2).

Substitute these values into the expression for f(2012)f(2012):
f(2012)=msin(α1)+ncos(α2)=1. f(2012) = m\sin(\alpha_1) + n\cos(\alpha_2) = -1.

Therefore, the answer is 1\boxed{-1}.

Solution 2

Since f(2011)=1f(2011) = 1, we have:
msin(2011π+α1)+ncos(2011π+α2)=1,m\sin(2011\pi + \alpha_1) + n\cos(2011\pi + \alpha_2) = 1,
which simplifies to msinα1ncosα2=1-m\sin\alpha_1 - n\cos\alpha_2 = 1. Therefore, we can deduce that msinα1+ncosα2=1m\sin\alpha_1 + n\cos\alpha_2 = -1.

Thus, f(2012)=msin(2012π+α1)+ncos(2012π+α2)f(2012) = m\sin(2012\pi + \alpha_1) + n\cos(2012\pi + \alpha_2)
=msinα1+ncosα2=1.= m\sin\alpha_1 + n\cos\alpha_2 = -1.

Therefore, the answer is 1\boxed{-1}.

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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.