2x² - 128
2(x² - 64), but (x² - 64) = x² - 8² (difference of 2 squares),[a²-b²=(a-b)(a+b)]
2(x² - 64) = 2(x² - 8²) = 2(x-8)(x+8)
Elite marathon race times improved from 5 to ~20 years, remained linear between ~20 and ~35 years, and started to increase at the age of ~35 years in a curvilinear manner with increasing age in both women and men. The sex difference in elite marathon race time increased non-linearly and was lowest at the age of ~49 years.
X/x+9 (original fraction)
x+1/ x+10 = 4/13
x+1=4 so x=3 and x+10=13 so again x=3
now that you have the value of x, substitute it into the original fraction to get:
3/12
