this involves a bit of work. In essence you have to determine the equation of a parabola given 3 pointd
Will use (1,8)(2,14)and (3,24)
the general form for a parabola (quadratic)is
y=ax^2 + bx +c
so can create 3 equations with 3 unknowns using the 3 points
1) 8= a+b+c. (when x=1 and y=8)
2) 14= 4a+2b+c(when x=2 and y=14)
3) 24=9a+3b+c( when x=3 and y=24)
subtract equation 2 from equation 3 which gives you
5a+b=10 (Equation 4)
subtract equation 1 from equation 2 which gives
3a +b=6((Equation 5)
subtract equation 5 fro equation 4 and you get
2a=4 so a = 2
If a =2 then b=0 and c=6 so equation is
y=2x^2 +6
15th term is 2(15^2)+6=2(225)+6= 456
