GCSE Edexcel Maths Paper 2 – The Final Question

So, the “GCSE Edexcel Maths Paper 2 – The Final” Question is out… We’d thought we’d had this year’s viral question with the carrot and tomatoes question! Little did we know, Edexcel still had some tricks up their sleeve. This tricky area question was even spotted on some A Level sites!

The skills needed are GCSE skills but, like last year’s Paper 1 geometry question, there are lots of different ways to approach it. It’s very easy to be unsure where to start!

The Question

Each of the octagons below is a regular octagon with sides of length \(a\).

Find the area of the shaded region. Give your answer in the form \(p(2 + \sqrt{2})a^2\).

The Answer

The shaded area can be split into a square and four identical triangles. So, to find the shaded area, we simply need to find the area of these smaller, simpler shapes.

Let’s start with the triangles.

We know they must be right-angled triangles because an exterior angle of a regular octagon is 45°, so the angles in each triangle must be 45°, 45° and 90°.

Each triangle has a base and height of length \(a\).

\(\begin{aligned}Area &= \frac{1}{2} \times a \times a\\&=\frac{1}{2}a^2\end{aligned}\)

There are four of these triangles, so their total area is \(4\times\frac{1}{2}a^2=2a^2\).

Now, we look at the square. To find its area, we need to find the length of a side.

As we can see, the length of the sections either side of the triangle are both \(a\) and the central section is the hypotenuse (\(h\)) of our triangle.

Using Pythagoras’ theorem, we get

\(\begin{aligned}h^2 &= a^2 + a^2\\&=2a^2\\h&= a\sqrt{2}\end{aligned}\)

So, each side of the square is \((2a + a\sqrt{2})\) units long.

Multiplying this by itself will give us the area of the square.

\(\begin{aligned}(2a + a\sqrt{2})(2a + a\sqrt{2})&= 4a^2 + 2a^2\sqrt{2} +2a^2\sqrt{2} + 2a^2\\&= 6a^2 + 4a^2\sqrt{2}\end{aligned}\)

Now, we just add on the area of the 4 triangles and then factorise the result.

\(\begin{aligned}6a^2 + 4a^2\sqrt{2} + 2a^2 &= 8a^2 + 4a^2\sqrt{2} \\&= 4(2 + \sqrt{2})a^2 \end{aligned}\)

So, did you find all that you were looking for in your investigation into the mystery the new “GCSE Edexcel Maths Paper 2 – The Final” Question? Whether you’re still mystified or not, we have a great range of helpful blogs here! You can also subscribe to Beyond for access to thousands of secondary teaching resources. You can sign up for a free account here and take a look around at our free resources before you subscribe too.

Leave a Reply