Intersections

Change one equation in this pair of simultaneous equations very slightly and there is a big change in the solution. Why?

Negatively Triangular

How many intersections do you expect from four straight lines ? Which three lines enclose a triangle with negative co-ordinates for every point ?

Which Is Cheaper?

When I park my car in Mathstown, there are two car parks to choose from. Which car park should I use?

Which Is Bigger?

Stage: 4 Challenge Level:

The ideas in this problem lead on from Which Is Cheaper?

Which is bigger, $n+10$, or $2n+3$?
How did you decide?

Charlie said:

"I wonder what happens when $n=4$."

"$4+10=14$ but $2 \times 4 + 3$ is only $11$."

"So it looks like $n+10$ is bigger."

Alison said:

"I wonder what happens when $n=10$."

"$10+10=20$ but $2 \times 10 +3$ is $23$."

"So it looks like $2n+3$ is bigger."

Can you explain why they have come to different conclusions?
Is there a diagram you could draw that would help?

For the following pairs of expressions, can you work out when each expression is bigger?

$2n+7$ and $4n+11$

$2(3n+4)$ and $3(2n+4)$

$2(3n+3)$ and $3(2n+2)$

Here are some challenges to try:

Find two expressions so that one is bigger whenever $n< 5$ and the other is bigger whenever $n> 5$.

Find three expressions so that the first is biggest whenever $n< 0$, the second is biggest whenever $n$ is between 0 and 4, and the third is biggest whenever $n> 4$.

Find three expressions so that the first is biggest whenever $n< 3$, the second is biggest when $n> 3$, and the third is never the biggest.

Find three expressions so that one of them is the biggest regardless of the value of $n$.

Click here for a poster of this problem.

Working systematically. Graphs. Transformation of functions. Graph plotters. Simultaneous equations. Mathematical reasoning & proof. Solving equations graphically. Inequality/inequalities. Cubic functions. Gradients.

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Intersections

Negatively Triangular

Which Is Cheaper?

Which Is Bigger?

Stage: 4 Challenge Level: