Copyright © University of Cambridge. All rights reserved.

'Mind Your Ps and Qs' printed from http://nrich.maths.org/

Show menu


Leo, Lily, Pippa and Lewis from Fakenham College sent us this entertaining solution

We transferred the equations onto cards so we could move them about easily. Good idea!

These are the ones we got to match, then we coloured them in and added glitter.Glittery maths? Excellent idea .

$ x< 0 \Leftrightarrow x\int^x_0 ydy < 0$

$x=0 \Rightarrow \int^x_0 \cos y dy =0$

$0< x< 1\Rightarrow \cos(x/2)> \sin(x/2) $

$x> 2\Rightarrow x^3> 1 $

$x> 4\Rightarrow 2\int^{x^2}_0ydy> x^2$

$x=-2\Rightarrow |x|> 1$

$x=1\Rightarrow x^2+x-2=0 $

We didn't manage to get four of < => , but were pleased we got this :)

You should be pleased! This was good logical thinking. These seven were all correct, but there was a mistake in an eighth one you included: $x^2+4x+4 =0 \Rightarrow x> 1$. Can you see why?

The full solution that we obtained was

$x^3> 1 \Leftrightarrow x> 1$
$2\int^{x^2}_0ydy> x^2 \Leftrightarrow |x|> 1$
$x=-2 \Leftrightarrow x^2+4x+4 =0$
$x=1\Rightarrow x^2+x-2=0$
$0< x< 1 \Rightarrow \cos(x/2)> \sin(x/2)$
$x> 4\Rightarrow x> 2$
$x< 0 \Leftrightarrow x\int^x_0 ydy < 0$
$x=0 \Rightarrow \int^x_0 \cos y dy =0$