10. Which of the following statements is true of f(x) =-13 - 612 -91 -2? a) f is decreasing on (-3, -1) b) f is increasing on (-3, -1) c) f is increasing on (-co, -3) d) f is increasing on (-2, 00) e) f is decreasing for all real values 11. Given that f(z) = -z? + 18x - 78 has a relative maximum at I = 9, choose the correct statement. a) f' is negative on the interval (-00, 9) b) f' is negative on the interval (9, co) c) f' is positive on the interval (9,co) d) f' is positive on the interval (-9, co) e) f' is positive for all real values 12. Find y given y? - 3zy + 2? = 7. 2x+ y 3y - 2r 2y - 3x 2y - 3x C) 3-2y d ) 7 e) 3x - 2y 3y - 21