If x = 1.5 is the only solution to the equation 4x² - ax + b =0 then
4x² - ax + b = 4(x - 1.5)² |use p² - 2pq + q² = (p - q)²
4x² - ax + b = 4(x² - 2x · 1.5 + 1.5²)
4x² - ax + b = 4(x² - 3x + 2.25)
4x² - ax + b = 4x² - 12x + 9 |subtract 4x² from both sides
-ax + b = -12x + 9
therefore
-a = -12 ⇒ a = 12 and b = 9
