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# If 3f(x) + 2f(−x) = 5x − 10, what is the value of f (1)?

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Joined: 02 Sep 2009
Posts: 52902
If 3f(x) + 2f(−x) = 5x − 10, what is the value of f (1)?  [#permalink]

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01 Oct 2018, 22:14
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Difficulty:

55% (hard)

Question Stats:

44% (01:55) correct 56% (02:37) wrong based on 35 sessions

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If 3f(x) + 2f(−x) = 5x − 10, what is the value of f (1)?

(A) 0
(B) 1
(C) 2
(D) 3
(E) 4

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Re: If 3f(x) + 2f(−x) = 5x − 10, what is the value of f (1)?  [#permalink]

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01 Oct 2018, 22:24
Bunuel wrote:
If 3f(x) + 2f(−x) = 5x − 10, what is the value of f (1)?

(A) 0
(B) 1
(C) 2
(D) 3
(E) 4

3f(x) + 2f(−x) = 5x − 10
2f(x) + 3f(-x) = -5x - 10

9f(x) + 6f(-x) = 15x - 30
4f(x) + 6f(-x) = -10x - 20

Subtract the above two equation -

5f(x) = 25x - 10
f(x) = 5x - 2
f(1) = 3

Hence, D.
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Re: If 3f(x) + 2f(−x) = 5x − 10, what is the value of f (1)?  [#permalink]

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01 Oct 2018, 22:50
2
1
Bunuel wrote:
If 3f(x) + 2f(−x) = 5x − 10, what is the value of f (1)?

(A) 0
(B) 1
(C) 2
(D) 3
(E) 4

If $$x=1$$, the equation becomes $$3f(1) + 2f(-1) = 5 - 10 = -5$$ -> (1)

If $$x=-1$$, the equation becomes $$3f(-1) + 2f(1) = -5 - 10 = -15$$ -> (2)

3*(1) - 2*(2) -> $$9f(1) - 4f(1) = -15 + 30 = 15$$ -> $$5f(1) = 15$$

Therefore, the value of f(1) = $$\frac{15}{5}$$ = 3(Option D)
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Re: If 3f(x) + 2f(−x) = 5x − 10, what is the value of f (1)?   [#permalink] 01 Oct 2018, 22:50
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# If 3f(x) + 2f(−x) = 5x − 10, what is the value of f (1)?

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