(2x+9)^2=64

Question

the percentage of adult height attained by a girl who is x years old can be odeled by f(x)=62+35log(x-4), where x represents the girl's age and f(x) represents the percentage of her adult height. Approximately what percentage of her adult height has a girl attained at age 13?

Answer 1

( 2x+9)^2 = 64

(2x +9)^2 -64 = 0

(2x+9)^2 - 8^2 = 0    ; ( a^2 - b^2 = ( a-b)(a+b)

(2x+9-8)(2x+9+8) = 0

(2x+1)(2x+!7) = 0

x = -  1/2 or x = - 17/2