Question

If f(x) = x2 − 1, and f(2a) = 35, then what could be the value of a ?

Answer 1

F(2a)=35
f(2a)=(2a)^2-1=35
(2a)^2-1=35
add 1 both sides
(2a)^2=36
sqrt both sides
2a=+/-6
divde 2
a=+/-3

a=3 or -3

Answer 2

When    f(x)=x^2-1
and       f(2a)=35    it means that:    x=2a
                                                     {   x^2-1=35

so: (2a)^2-1=35
      4(a^2)-1=35
      4(a^2)=35+1
      4(a^2)=36    /4
       a^2=9      
       a=3