Christian Lawson-Perfect

Christian Lawson-Perfect on Factorising Quadratic Equations with $x^2$ Coefficients Greater than 1 8 years, 5 months ago

Gave some feedback: Has some problems

Christian Lawson-Perfect on Factorising Quadratic Equations with $x^2$ Coefficients Greater than 1 8 years, 5 months ago

Saved a checkpoint:

The statement says you can factorise as $(ax+m)(bx+n)$ but then part a asks you to factorise in the form $a(x+m)(x+n)$. Should this be a separate question, since spotting a common factor of all the coefficients is a fairly simple corollary of factorising a quadratic with leading coefficient 1?

In fact, part b is the same! I was shown $8x^2+240x+1600=0$, which factorises as $8(x+10)(x+20) = 0$. The expected answer had roots $-5/4$ and $-5/2$, which is equivalent to $8x^2+30x+25=0$. So is it the displayed equation that's wrong?

The marking for part a is wrong - I think the wrong variable is used somewhere, but it's not obvious where.

Part b could begin by asking you to find the factorisation.

In part c, I got $2x^2+13x+20$, so a particularly pedantic student might want to leave the second gapfill empty, since the coefficient of $x$ in the second part is $1$. Can you make sure that the coefficient of $x^2$ in the equation is greater than $2$?

I got $-5/3$ as one of my roots in part d, so I've enabled "allow the student to enter a fraction".

Parts c and d could use the same equation - why not? That would make a nice, self-contained question.

So, in summary:

• Fix the marking in parts a and b.
• If they use the same equation rather than a new one in each part, I think parts (a,b) make a self-contained question, and (c,d) another.

Christian Lawson-Perfect on Complete a frequency table and find the measures of central tendency 8 years, 5 months ago

Gave some feedback: Ready to use

Christian Lawson-Perfect on Complete a frequency table and find the measures of central tendency 8 years, 5 months ago

Saved a checkpoint:

Never say something "prevents us from making mistakes" - a sufficiently stupid student always exists! Instead, say it "helps to make mistakes less likely".

I've done some fiddling with the advice, but otherwise this is a good question.

Christian Lawson-Perfect on Dividing a polynomial with remainders, using algebraic division 8 years, 5 months ago

Gave some feedback: Ready to use

Christian Lawson-Perfect on Dividing a polynomial with remainders, using algebraic division 8 years, 5 months ago

Saved a checkpoint:

Can we assume that the students have already seen long division of numbers?

I've rewritten the statement a bit. 

"We then repeat these same steps with the new polynomial until we are only left with an integer. " isn't strictly true - the remainder is a polynomial of lower degree than the divisor.

I reckon the statement text is better off in the advice.

The advice is quite lengthy, but I don't know if it's possible to do any better. 

Christian Lawson-Perfect commented on Find and use the formula for a geometric sequence 8 years, 5 months ago

And like the other sequences questions, the advice would benefit hugely from a table.

Christian Lawson-Perfect on Find and use the formula for a geometric sequence 8 years, 5 months ago

Gave some feedback: Has some problems