To think the text book is wrong

[trinesrad]

OK, long story short, offspring the younger fluncked out of his uni course last year and has now changed to physics. Due to his grades not being high enough when he left school (Higher Grade C (Scotland)), he has to d a summer school prior to starting. So to help him out we got him maths and physics revision books for higher, but we think this equation's answer is incorrect.

fx =2x+3
where x= -4

we all get the answer of -5 whereas the book is saying +9. Are we going mad?

Are you able to send a pic. Because it looks confusing.

fx=-5

But that would make f=1.25 if x=-4

Agree - can we have a pic? What you have done is just solved the equation, but the fx on the other side complicates things and in this context makes no sense.

Does it say fx = 2x + 3, in which case f is the unknown that you need to calculate? or f(x) = 2x + 3 in which case you are calculating the function of x?

Either way the answer isn't 9...

I get -9!

It is -5, the book is incorrect

so apparently its graph stuff which i am clueless about. here are pics of the question and answer. Its quicktest 1 question 2.

Thanks

You can essentially ignore the F(x), its just another way of writing y which is the ‘answer’. So if you replace it with y the equation is
Y=2x+3
y=2(-4)+3
y=-8+3
y=-5

....or at least that’s what a brief YouTube video I just watched said 😂

I think the fact that it is to with graphs changes the whole thing tbh rather than if it were just a simple equation

You are right, answer book is wrong.
Pretty confident, (have a maths degree).

I can't see the pictures very well, but it looks like you've found x, which is -5, but the question is actually asking you to find b?

SpikeDearheart apparently b is due to being a point on a map

But that could just be me struggling to see the question on my crappy broken phone

Thank you everyone

-5 is the correct answer

-5 is correct. Textbook is wrong. It happens sometimes.

-5 would be the correct answer if this were algebra and f was a variable. But this isn't algebra, it's either calculus (or trigonometry?) and f is not a variable, it denotes 'function'.

I am so rusty with this!

-5 It is still the correct answer.
It is just another way of effectively asking the same question.

Thanks for the pic - yes agree with the others. Book is unfortunately incorrect.

@horizondawn02

You can essentially ignore the F(x), its just another way of writing y which is the ‘answer’. So if you replace it with y the equation is Y=2x+3 y=2(-4)+3 y=-8+3 y=-5

....or at least that’s what a brief YouTube video I just watched said 😂

This is what I did in my head. But I'm 35 and haven't used equations for since I was 18!

Correct answer is -5. I would love to know how @Persephoned got 9

The answer is definitely -5.

I'm guessing it's a misprint as the second part of the question also has -4 for x.