C1 and C2 DOUBTS HERE!!!!!

[elemis]

I read your explanation, but see, in part (c) we found that the total of the allowances up to and including her 18^th birthday was 39600...how come her allowance would stop at the age of 26 at 32000? It's supposed to increase, right?

& one more question please:

In the specimen paper, [it has no particular date info, so I'll type the question here]:

The curve C has equation y=f(x) and the point P (3,5) lies on C.
Given that f'(x) = 3x²-8x+6

(a) Find f(x)
The answer is f(x)=x³-4x²+6x-4

(b) Not needed now

The point Q also lies on C, and the tangent to C at Q is parallel to the tangent to C at P.
(c) Find the x-coordinate of Q.

I found the gradient to be 9 [using the formula for f'(x)]
& it's correct according to the marking scheme.

And then I equated the formula:
3x²-8x+6=9

I got 2 solutions: x=3, x=-1/3

Which one would be the correct one? The MS says it's -1/3 but I don't understand why!

Its -1/3 since you already know the coordinates of P i.e. it is 3,5

[**RoRo**]

Its -1/3 since you already know the coordinates of P i.e. it is 3,5

OHHHHHH!!

OMG! That's so stupid of me!

& I've spent like half an hour trying to figure out why did the Mark Scheme say so!!

Thanks a lot!! 

[Helium]

Hello

Anyone mind,

Q)Perry left school driving towards the lake one hour before jaidee.
jaidee drove in the opposite direction going 6mph slower then perry for one hour after which time they
were 174 min apart. What was perry's speed.

I'm stuck.

[astarmathsandphysics]

https://studentforums.biz/math-146/m1-doubts-here!!!!/300/

[**RoRo**]

In January 2010, Question 10 (b), I'm getting my answer as -3<k<1/4 and the equation that I have used is b²-4ac=0 where the value of a = 1, b= 4k and c = 3 +11k.

In the marking scheme, the answer is -1/4<k<3 and they've got some really weird explanation, check this link: http://www.scribd.com/doc/29694732/Edexcel-GCE-January-2010-Core-Mathematics-1-C1-Marking-Scheme

Can someone please explain this to me?

Thanks!

[Freaked12]

Dude why did you use b^2-4ac=0??
you have to use b^2-4ac<0
b^2 - 4ac is less than zero, then there are no solutions. This means that there are no values of x giving a value of y of zero, hence the graph of the curve will not cross the x-axis.
b^2 - 4ac = 0 then there are two equal values for x (that is, the
line of the graph touches the x-axis once)


your result would match the mark scheme if you had used the correct formula.

Hope this helps

[**RoRo**]

I didn't understand what you wrote in bold! :/

[Freaked12]

I was just saying by equating b^2-4ac to zero, you are showing that the equation has one solution but the question is saying find all the values of k where where roots are not real so this is wrong.

you have to write b^2-4ac<0 to show there are no real roots of K.

This will ultimately answer your questioin

[Freaked12]

I re-edited the post By the way

[**RoRo**]

I was just saying by equating b^2-4ac to zero, you are showing that the equation has one solution but the question is saying find all the values of k where where roots are not real so this is wrong.

you have to write b^2-4ac<0 to show there are no real roots of K.

This will ultimately answer your questioin

Ohhh...yes, yes, yes!

Thank you for the clarification!

[HUSH1994]

what is a range,domain,and one-one funtion,and in this question:
given that f:x- 2x^2 + 8x-18
find the least value of k for which f is one-one,how do u do it?

[blackberry]

heyy guys i have a doubt, its from the c1 textbook, chapter 2, mixed exercise 2G, Q.5

Given that for all values of x: 3x²+12x+5=p(x+q)² +r

a)find the values of p,q and r
b)solve the equation 3x²+12x+5=0
---------------------------------------------------------------------------------------
a)i got this one!
b)i tried using the quadratic formula to solve it and i got -2+(1/3)(surd 21) however the answer is -2+(surd7/surd3). The answer was obtained by completing the square. When i solved both the answers using a calculator the answers were the same.
This question is from a past paper but i dont know which one, and i need to know if my answer is acceptable as the textbook doesnt mention it, so can anyone tell me which past paper this question if from??
thanxx!

[The Golden Girl =D]

heyy guys i have a doubt, its from the c1 textbook, chapter 2, mixed exercise 2G, Q.5

Given that for all values of x: 3x²+12x+5=p(x+q)² +r

a)find the values of p,q and r
b)solve the equation 3x²+12x+5=0
---------------------------------------------------------------------------------------
a)i got this one!
b)i tried using the quadratic formula to solve it and i got -2+(1/3)(surd 21) however the answer is -2+(surd7/surd3). The answer was obtained by completing the square. When i solved both the answers using a calculator the answers were the same.
This question is from a past paper but i dont know which one, and i need to know if my answer is acceptable as the textbook doesnt mention it, so can anyone tell me which past paper this question if from??
thanxx!

I did it by Completing the Square . you can do it by Quadratic formula or completing the Square ,both are correct

x²+ 4x + 5/3
x² + 4x + (2)² - (2)² + 5/3 =0
[x+2]²- 4 + 5/3
[x+2]²= 7/3
x+2 = positive negative surd 7/3
x= -2 positive or negative surd 7/3

Therefore ;

x = -2+ surd 7/3           OR        x= -2-surd 7/3

Let me know if you don't get it

[blackberry]

well i know how to do it by completing the square but what i meant was:
quadratic formula answer : -2+(1/3)(surd21)= -0.472
square completion answer: -2+(surd7/surd3)= -0.472

they want us to express the answer in surd form, so my answer is the quadratic formula one and the one they mentioned in the textbook was the square completion one. Even though they both give the same answer i.e. -0.472, i wanted to know if my answer in surd form is acceptable by the examiners so i wanted to know which paper this q is from??

thanxxx for the help!!! <3

[The Golden Girl =D]

I'm Sorry but I didn't get what you want :S ?