Functions

[kreshnik]

$\displaystyle f(x)=2x-1\;\;\;\;\;f(a)=7\;\;\;\;\;\;\;f(7-a)=?$

attempted:

$\displaystyle f(7)=2*7-1=13$

$\displaystyle f(7-a)=13-7=6$

I think it's wrong because none of my multiple choices doen't match!

 

[srmichael]

$\displaystyle f(x)=2x-1\;\;\;\;\;f(a)=7\;\;\;\;\;\;\;f(7-a)=?$

attempted:

$\displaystyle f(7)=2*7-1=13$

$\displaystyle f(7-a)=13-7=6$

I think it's wrong because none of my multiple choices doen't match!

I'm not sure I follow how f(a) = 7. f(a) = 2a - 1

F(7-a) = 2(7-a) - 1 = 14 - 2a - 1 = 13 - 2a

 

[werd]

is one of the answers 5?

I think to help you answer this question you need to remember that this rule applies here: if f(y) = f(z) then y=z.

 

[lookagain]

$\displaystyle f(x)=2x-1\;\;\;\;\;f(a)=7\;\;\;\;\;\;\;f(7-a)=?$

attempted:

$\displaystyle f(7)=2*7-1=13$

$\displaystyle f(7-a)=13-7=6$

I think it's wrong because none of my multiple choices doen't match!

kreshnik,

what about this?

f(x) = 2x - 1

f(a) = 7


So 7 = 2(a) - 1

7 = 2a - 1

8 = 2a

4 = a


Then f(7 - a) =

f(7 - 4) =

f(3) =

2(3) - 1 =

6 - 1 =

5

 

[burakaltr]

$\displaystyle f(x)=2x-1\;\;\;\;\;f(a)=7\;\;\;\;\;\;\;f(7-a)=?$

attempted:

$\displaystyle f(7)=2*7-1=13$

$\displaystyle f(7-a)=13-7=6$

I think it's wrong because none of my multiple choices doen't match!

f(x)=2*x-1

f(a)=7

f(7-a)=b

2a-1=7

a=4

f(3)=?

 

[kreshnik]

kreshnik,

what about this?

f(x) = 2x - 1

f(a) = 7


So 7 = 2(a) - 1

7 = 2a - 1

8 = 2a

4 = a


Then f(7 - a) =

f(7 - 4) =

f(3) =

2(3) - 1 =

6 - 1 =

5

Well I think you're right...

$\displaystyle A)\;5$
$\displaystyle B)\;8$
$\displaystyle C)\;7$
$\displaystyle D)\;14$

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Example:
$\displaystyle f(x)=2x^2-\frac{17}{9}.\;\;\;\text{Find:}\;f(a)-f(a+2)$

I did...

$\displaystyle f(a)=2a^2-\frac{17}{9}$

$\displaystyle f(a+2)=2(a+2)^2-\frac{17}{9}$

$\displaystyle f(a)-f(a+2)=(2a^2-\frac{17}{9})-[2(a+2)^2-\frac{17}{9}]=$ $\displaystyle 2a^2-\frac{17}{9}-2(a^2+4a+4)+\frac{17}{9}=2a^2-2a^2-8a-8=-8a-8$

And Yes.. there is number 5 in multiple choice of the task nr 1. Thank you everyone for helping me.