1. EXAMPLE 3 Use the quadratic formula y = 10x 2 – 94x + 3900 4200 = 10x 2 – 94x – 3900 0 = 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 + 3900 where x is the number of years since 1971. In what year were 4200 films produced ? FILM PRODUCTION

2. EXAMPLE 3 Use the quadratic formula Substitute values in the quadratic formula: a = 10, b = –94, and c = –300. 20,836 94 + – 20 = Simplify. The solutions of the equation are: ANSWER There were 4200 films produced about 12 years after 1971, or in 1983. x = (–94) 2 – 4 (10)(–300) –(–94) + – 2(10) 94 + 20,836 20 12 94 –20,836 20 –3. and

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