If f(x) = x2 − 1, and f(2a) = 35, then what could be the value of a ?
Answers;
-6
-3
1
2
6
Can somebody explain please?

Question

If f(x) = x2 − 1, and f(2a) = 35, then what could be the value of a ?
Answers;
-6
-3
1
2
6 
Can somebody explain please?

anonymous · Answer

Thank you.

whpalmer4 · Answer

$$f(x) = x^2-1$$That means to find the value of the function at any value of $x$, we square $x$ and subtract 1.  If $x = 2a$, we square $2a$ and subtract 1:
$$f(2a) = (2a)^2-1 = 4a^2-1$$Now, we know that $f(2a)=35$so we can find the value of $a$:
$$f(2a) = (2a)^2-1 = 4a^2-1=35$$$$4a^2-1+1=35+1$$$$4a^2=36$$$$a^2=9$$$$a=\pm3$$

whpalmer4 · Answer

Note that $a=3$ would also be a valid answer, if it appeared in the list of answer choices.