EXAMPLE 3 Use the quadratic formula y = 10x 2 – 94x = 10x 2 – 94x – = 10x 2 – 94x – 300 Write function. Substitute 4200 for y. Write in standard form. SOLUTION For the period 1971  2001, the number y of films produced in the world can be modeled by the function y = 10x 2  94x where x is the number of years since In what year were 4200 films produced ? FILM PRODUCTION

EXAMPLE 3 Use the quadratic formula Substitute values in the quadratic formula: a = 10, b = –94, and c = – , – 20 = Simplify. The solutions of the equation are: ANSWER There were 4200 films produced about 12 years after 1971, or in x = (–94) 2 – 4 (10)(–300) –(–94) + – 2(10) , –20, –3. and

GUIDED PRACTICE for Example 4 WHAT IF? In Example 3, find the year when 4750 films were produced. 4. ANSWER 1986