Answer:
B) 5
Step-by-step explanation:
We are given the function:
[tex]f(x)=x(x+3)[/tex]
We are given that f(a) = 40 and a > 0 and we want to determine the value of a.
Substitute:
[tex]f(a)=40=a(a+3)[/tex]
Distribute:
[tex]a^2+3a=40[/tex]
Subtract 40 from both sides:
[tex]a^2+3a-40=0[/tex]
We can factor using 8 and -5. Hence:
[tex](a+8)(a-5)=0[/tex]
By the Zero Product Property:
[tex]a+8=0\text{ or } a-5=0[/tex]
Solve for each case:
[tex]\displaystyle a=-8\text{ or } a=5[/tex]
Since a > 0, we can eliminate the first solution. Hence:
[tex]a=5[/tex]
Our answer is B.
