"When are we going to use this stuff in real life, Sir?" asks a Year 9 pupil, staring at the half-expanded brackets on his page.
"You'd better hope someone has used maths in real life," I reply.
"Your mobile phones and computer games wouldn't work without itI it's everywhere."
For maths teachers, this is probably a familiar scenario. But once outside the classroom, pupils encounter few people who expound positive practical reasons for studying maths.
So to help the cause, I decided to call for back up from some of Europe's top company chief executive officers. I spent an evening emailing and writing to ask why maths was so important in their business. The response was immediate and the opinions united. Maths means creative thinking skills.
BT CEO Ben Verwaayen replied instantly. He said: "Maths is all about training your brains into logic. My strong advice is to do whatever it takes to get on with it."
Boots CEO Richard Baker said: "We would be lost without people with good maths skills."
Tesco director David North interviewed staff on their need for maths.
"People who can use and understand numbers are important to Tesco," he concluded in a detailed two-page letter.
Erica Tyson from Rolls Royce writes that the company values "the creative problem-solving skills that are developed through the study and practice of mathematical concepts."
Alan Giles, chief executive of HMV and Waterstone's, said: "We believe that a sound knowledge of maths helps our employees think logically and objectively, and helps us make better decisions."
From Finland, on behalf of the mobile phone company which employs 53,000 people worldwide, Nokia vice president Arja Suominen added: "Maths is not only numbers, but also a way of thinking and solving problems - skills that everyone needs. We could never have become the world leading mobility company we are today if it wasn't for skilful people who had the creative thinking power to look for new ideas beyond existing products, services and ways of working."
These people don't just talk a good maths story, they've lived it. Richard Baker did A-level maths and is an engineering graduate. He now manages 54,000 employees, with sales of more than pound;5 billion in 130 countries. "It's true that we have ever-improving calculators, computers and other devices to help us with numbers," he says. "But without a good grasp of mathematical principles, we wouldn't understand fully how to operate those tools, nor would we know how to interpret them."
HMV's Alan Giles is a physics graduate. He now runs HMV Group, employing more than 13,000 people in 10 countries. He says: "I feel strongly about this, having studied maths (a long time ago) at my local comprehensive school, and - at the time - wondering what the point was. Not only did I gradually pick up what the subject was about, but I also began to enjoy it."
To make the most of these responses and really get the message across, the letters have been reproduced as wall posters and are used in PowerPoint presentations; they are also being summarised in the school newsletter. To read the letters, go to www.pifactory.co.uk.
David Whitfield is a maths teacher at Southgate School in Enfield, north London