Q: Solve x^2 - 8x + 15 = 0 by factorisation. Step 1: Find two numbers: multiply to 15, add to -8. Try -3, -5: (-3)(-5) = 15, -3 + (-5) = -8. ✓ Step 2: Factor: (x - 3)(x - 5) = 0. Step 3: x - 3 = 0 gives x = 3; x - 5 = 0 gives x = 5. Step 4: Check x = 3: 9 - 24 + 15 = 0. ✓