VCE Methods Question Thread!

[grannysmith]

Thanks guys, but I'm still really confused on how to structure a worded response! Where does the 2 come from?  why is it 2A+2B=20?

And yes i have done simultaneous equations.

Okay.
Let width = w
Let length = l
Let perimeter = P

The perimeter = 2 x width + 2 x length
Therefore we can say P = 2w + 2l

We know that the perimeter is 20, so 2w + 2l = 20. That's one equation

Edit: clarified by IndefatigableLover :p

[IndefatigableLover]

Thanks guys, but I'm still really confused on how to structure a worded response! Where does the 2 come from?  why is it 2A+2B=20?

And yes i have done simultaneous equations.

So you know that the perimeter of a rectangle equals 20.
If you label one side as 'A' and another side 'B' then the perimeter of the rectangle is 2A +2B = 20

Because the perimeter consists of adding of all the sides and a rectangle has four sides, you've only accounted for two so far. But there are two widths and two lengths to be accounted for thus there is a '2'.

Edit: Beaten by Oddly

[Only Cheating Yourself]

So you know that the perimeter of a rectangle equals 20.
If you label one side as 'A' and another side 'B' then the perimeter of the rectangle is 2A +2B = 20

Edit: Beaten by Oddly

Still not sure where the 2A and 2B come from, i haven't done much perimeter before as that a formula or something?

[IndefatigableLover]

Still not sure where the 2A and 2B come from, i haven't done much perimeter before as that a formula or something?

It's just like this image here but replace 'l' and 'w' with 'A' and 'B' really...
They've just labelled it differently because they've specified it like that.

[lzxnl]

Can someone help me with spotting my misconception/mistake here?






divide both sides by log e



Actual answer: k = In (4)


EDIT: Made working clearer

The log_e is a function; you can't cancel it.

[M_BONG]

The log_e is a function; you can't cancel it.

But can you cancel log10? because my book cancelled log10 once in one of its worked examples.

[TrueTears]

Think of it like this. Take any generic function , is it true that ? Now let .

[Bluegirl]

Stuck, again.
Have to solve the pairs of simultaneous equations.

Do I transpose it first or make a common factor?

3/2x - y= 4

1/2x + 3/4y = 10

And this one:

x/3 + y/2 = 11

x- y/3 = 22

Thankyou

[brightsky]

To solve a system of two linear equations:
1. Take one equarion. Rearrange to make y the subject.
2. Substitute the rearranged equation above into the other equation. Solve for x.
3. Substitute the value of x into one of the equations. Solve for y.

[lzxnl]

But can you cancel log10? because my book cancelled log10 once in one of its worked examples.

You can't directly cancel it either.
You book may have done log (a) = log(b) => a=b
That's raising both sides to the base of the log.
If you have 2 ln(a) = ln(b)
you can't say 2a=b.

[Bluegirl]

To solve a system of two linear equations:
1. Take one equarion. Rearrange to make y the subject.
2. Substitute the rearranged equation above into the other equation. Solve for x.
3. Substitute the value of x into one of the equations. Solve for y.

Thanks

Is that better than the elimination method?

[lzxnl]

Debatable. Depends on the question. For linear equations, I prefer elimination. In general though, for non linear equations, substitution will nearly always work.

[brightsky]

Thanks

Is that better than the elimination method?

Substitution method is more systematic, and can be used to solve linear systems in more than two variables quickly and efficiently.

[Bluegirl]

Substitution method is more systematic, and can be used to solve linear systems in more than two variables quickly and efficiently.

So it's the same method for a system of linear equations with more than 2 variables?

[lzxnl]

Substitution method is more systematic, and can be used to solve linear systems in more than two variables quickly and efficiently.

Really? I still eliminate one by one to be honest for those.