Maths Methods 3/4 Help Thread 2011

[ech_93]

I have a question....
The mass of a radioactive element is described by where represents the mass in grams after years. If the initial mass is 500 grams and the mass at 10 years is 400 grams, find the value of .

Thanks

[m@tty]

So they give you the relationship

and two points:





Sub the first point and you'll get ; then sub the second point and solve for k.

[ech_93]

^ I tried that but I didn't get the right answer

[pi]

I have a question....
The mass of a radioactive element is described by where represents the mass in grams after years. If the initial mass is 500 grams and the mass at 10 years is 400 grams, find the value of .

Thanks

[kefoo]

y = sin(x) + 2cos(x)
(x = theta)

Not sure on Addition of Ordinates  :S

[Aurelian]

y = sin(x) + 2cos(x)
(x = theta)

Not sure on Addition of Ordinates  :S

I assume you're wondering how to graph this via addition of ordinates...?

If so, basically the best way to go about addition of ordinates is to firstly locate all the key points. So, wherever one of the component graphs has a y value of 0, the y value of the overall graph will be equal to that of the second graph, and vice versa. Similarly, where the two component graphs intersect, you know the overall value will be double that value at intersection. Further, at least for sketching purposes, you know that x-intercepts will occur when the value of one of the graphs is directly equal in magnitude to the value of the other graph, but negative in its sign (to actually find out the points of these intercepts you'll need to do some calculations, though).

Not really sure what else to say, but hopefully that's been at least a little helpful!

[Respect]

uhh i have a  question which is confusing me.  and idk how to do.. these two questions.. 6 (idk how) .. but 7 .. cant we make the root into, x +2 and hence the derivative is 1??  why nt.

and can someone solve em. thanks.

[xZero]

6) use chain rule and you should get

7) chain rule again,

and to answer your question regarding 7, , not

[Respect]

6) use chain rule and you should get

7) chain rule again,

and to answer your question regarding 7, , not

ohh k. thanks makes sence.

[ech_93]

I have another question;
Find the equation of the polynomial function that goes through the points (-4,0), (-3,2), (-1,7), (-1,3) if it exists.

I'm not sure where to start. You don't have to work it all out, but could someone just tell me where to start?!

Thanks

[xZero]

you sure you typed the points correctly? a polynomial function can not contain both (-1,7) and (-1,3)

[ech_93]

Yep, the points are right.
Just checked the answer, it says "The function does not exist". Probably should have checked that before I asked...

Thanks anyway

[ech_93]

Actually, just say the function did exist (with different points, obviously) how would you go about finding the equation. It confuses me because it just says polynomial, rather than cubic or something.
How would you work it out :S

[xZero]

well if you're given 4 points and nothing else I'm going to assume the function is a cubic/parabola/linear

The general equation is y=ax^3+bx^2+cx+d, sub the points in and solve for a,b,c,d

Just remember you need 2 points for a linear equation, 3 points for parabola, 4 points for cubic etc

[ech_93]

If , then what does y equal?