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Error in Text Book?

The curve y = 1 + ( 1 / 2+x) crosses the x axis at point A and the y axis at point B.

(a) Calculate the coordinates of A and of B.

Done this, they are A = (0, 1.5) and B = (-3, 0) checked the answer and this is correct

(b) Find the equation of the line AB.

Gradient of AB = y1-y2 / x1-x2 = 1.5-0 / 0-(-3) = 1.5/3 = 1/2

Therefore y = 1/2 x + c

Using (0, -3):
-3 = 1/2 x 0 + c
c = -3

Thus

y = 1/2 x - 3

multiply all by 2 to remove fractions

2y = x - 6

this can be rearranged to

x - 2y - 6 = 0

I'm pretty sure this is correct. But the text book says the answer is x - 2y +3 = 0???
What do you guys think?
its possible the txtbook is wrong....

our chemistry one is full of them....get a few other people to work it out and if you all get the same answer...then assume its wrong
The answer is x-2y+3=0 since the coordinate you have chosen to use is (0, -3), where as you should have used (-3, 0) which you calculated in in part (a). It is just a simple error and your calculation is perfectly correct.
Note: (0, -3) does not belong to the curve y = 1 + ( 1 / 2+x) which can be checked simply by substituting the values in to the equation.
(edited 13 years ago)
Original post by RamsFanNo1
The answer is x-2y+3=0 since the coordinate you have chosen to use is (0, -3), where as you should have used (-3, 0) which you calculated in in part (a). It is just a simple error and your calculation is perfectly correct.
Note: (0, -3) does not belong to the curve y = 1 + ( 1 / 2+x) which can be checked simply by substituting the values in to the equation.


Thanks,

I've been doing this so much :frown:(!

Just started teaching myself maths again after being out of school for 3 yrs been doing c1 for about 4 days now. I get it and can do it but keep doing stupid stuff like that!!
Original post by Bleak Lemming
Thanks,

I've been doing this so much :frown:(!

Just started teaching myself maths again after being out of school for 3 yrs been doing c1 for about 4 days now. I get it and can do it but keep doing stupid stuff like that!!


Don't worry about it, we all make silly mistakes from tiem to time. To be honest it is good that you make these mistakes, because it is these which you will learn from and will not make again in the future. I wish you all the luck with learning A level maths and if you do ever have any problems, then feel free to ask me, I am always happy to help.

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