Find the roots of the equation x² − 3x − 10 = 0.

Correct answer: 5, −2. Factorising gives (x − 5)(x + 2) = 0, so x = 5 or x = −2.

Background: Find two numbers with product −10 and sum −3: that is −5 and +2.

• −8, −3: −8 and −3 do not satisfy the equation.
• 9, 4: 9 and 4 do not satisfy the equation.
• 4, 8: 4 and 8 do not satisfy the equation.

Did you know? Check: 25 − 15 − 10 = 0.

Memory trick: Product −10, sum −3.