VCE Methods Question Thread!

[Eric11267]

For y=-5cost(pi*t/8)+5, why do we let cos(pi*t/8)=-1 to find t, when y is first at its maximum?

I thought max of cos(x) was 1, not -1

The max of cos(x) is 1, that is correct. But when you add the -5 at the beginning, you're essentially 'flipping' the graph and reflecting it in the x axis. So when cos(pi*t/8)=1 that would give you the minimum of 0 and if cos(pi*t/8)=-1 that would give you the maximum of 10. Hope this helps, ask if you need more clarity

[atar.notes.user]

probably a really stupid question, but how do i do q7 MCQ of 2012 exam 2 (vcaa)
i keep getting c (20) as the answer

also how do i do q 16 of MCQ (Same paper)?

[Eric11267]

probably a really stupid question, but how do i do q7 MCQ of 2012 exam 2 (vcaa)
i keep getting c (20) as the answer

also how do i do q 16 of MCQ (Same paper)?

7. This is an average value of a function question, and your terminals will be 2 and 14
16. Exactly one solution occurs when either both turning points are above the x axis, or both turning points are below the x axis. Look at the y coordinates of the turning points provided and figure out what needs to be added to move them both above or below the axis

[uhoh]

The max of cos(x) is 1, that is correct. But when you add the -5 at the beginning, you're essentially 'flipping' the graph and reflecting it in the x axis. So when cos(pi*t/8)=1 that would give you the minimum of 0 and if cos(pi*t/8)=-1 that would give you the maximum of 10. Hope this helps, ask if you need more clarity

thanks so much 

when a question references upper rectangles for approximation, that's right approximation, yeah? So if it references lower rectangles, would that be left approximation?

[Eric11267]

thanks so much 

when a question references upper rectangles for approximation, that's right approximation, yeah? So if it references lower rectangles, would that be left approximation?

I've never seen a question using the terms 'upper' and 'lower' for describing approximations, so I doubt you will get anything on it on the real exam. If I had to take a guess, I'd assume upper would be right rectangle for an increasing function and left rectangle for a decreasing one. But again, I doubt its something you will encounter. If I'm wrong, someone feel free to correct me.

[Jessica1231]

The line with equation y=mx is tangent to the circle with centre (10,0) and radius 5 at the point p(x,y)
b) show that the x-coordinate of the point P satisfies the equation (1+m^2)x^2-20x+75=0
c) use the discriminant for this equation to find the exact value of m
d) Find the coordinates of P (2 points)
e) FInd the distance of P from the origin

Can someone briefly explain question 2? Like am I supposed to let x be x??

[uhoh]

To solve for (x^2-3x+2)/(x^2-1)=0, why can't you just let (x^2-3x+2)=0? Why do you have to factorise first?

[Shadowxo]

To solve for (x^2-3x+2)/(x^2-1)=0, why can't you just let (x^2-3x+2)=0? Why do you have to factorise first?

Because 0/0 is undefined. An alternative way to solve it is to let x^2-3x+2=0 but say the denominator can't equal zero, so x ≠ 1 or -1.
If you solved without doing this, you'd find x = 1 or 2 but you'll find if you have x=1 it'll result in 0/0 as the denominator is 0 as well.

The line with equation y=mx is tangent to the circle with centre (10,0) and radius 5 at the point p(x,y)
b) show that the x-coordinate of the point P satisfies the equation (1+m^2)x^2-20x+75=0
c) use the discriminant for this equation to find the exact value of m
d) Find the coordinates of P (2 points)
e) FInd the distance of P from the origin

Can someone briefly explain question 2? Like am I supposed to let x be x??

So for b), we know y=mx and (x-10)²+y²=25
We know at the point of intersection, the y values are the same and the x values are the same. So we can simply substitute y=mx into the circle equation.

If you need help with any of the other parts feel free to ask (I assumed you needed help with b because you said question 2 but more than happy to help with the other parts)

[uhoh]

Thanks shadowxo! Have to check that the denom isn't equal to 0

[snowisawesome]

If i'm bad at maths, but if i do every single textbook question in the methods textbook, can I get a 40 raw?

[Bri MT]

If i'm bad at maths, but if i do every single textbook question in the methods textbook, can I get a 40 raw?

I doubt it, unless you are able to understand what you are doing & use it in application questions.

You're much better off  spending most of your time on VCAA questions, not textbook ones.

[uhoh]

For this exam 1 question, how do I know what the graph looks like and whether the median is before or after the mode?
1st image: eqn, 2nd image part iv): question (not sure if you need to do ii and iii to find iv though) and 2nd image: Ans

And for sign tables, do we need to write the corresponding value of dy/dx for an x value (apart from when dy=dx=0)? Or can we just write dy/dx= positive/ negative? e.g. x=2, dy/dx= 3 (or can we just write dy/dx=+ve)

[snowisawesome]

I doubt it, unless you are able to understand what you are doing & use it in application questions.

You're much better off  spending most of your time on VCAA questions, not textbook ones.

Even if i have a tutor?

[atar.notes.user]

is there a mistake in Q8 2013 VCAA exam 1??

the continuous function doesnt have x multiplied to cos in it

[uhoh]

is there a mistake in Q8 2013 VCAA exam 1??

the continuous function doesnt have x multiplied to cos in it

Nah you need to multiply the function by x to find E(x)