Answer:
Option a.
Step-by-step explanation:
By looking at the options, we can assume that the function y(x) is something like:
[tex]y = \sqrt{4 + a*x^2}[/tex]
[tex]y' = (1/2)*\frac{1}{\sqrt{4 + a*x^2} }*(2*a*x) = \frac{a*x}{\sqrt{4 + a*x^2} }[/tex]
such that, y(0) = √4 = 2, as expected.
Now, we want to have:
[tex]y' = \frac{x*y}{2 + x^2}[/tex]
replacing y' and y we get:
[tex]\frac{a*x}{\sqrt{4 + a*x^2} } = \frac{x*\sqrt{4 + a*x^2} }{2 + x^2}[/tex]
Now we can try to solve this for "a".
[tex]\frac{a*x}{\sqrt{4 + a*x^2} } = \frac{x*\sqrt{4 + a*x^2} }{2 + x^2}[/tex]
If we multiply both sides by y(x), we get:
[tex]\frac{a*x}{\sqrt{4 + a*x^2} }*\sqrt{4 + a*x^2} = \frac{x*\sqrt{4 + a*x^2} }{2 + x^2}*\sqrt{4 + a*x^2}[/tex]
[tex]a*x = \frac{x*(4 + a*x^2)}{2 + x^2}[/tex]
We can remove the x factor in both numerators if we divide both sides by x, so we get:
[tex]a = \frac{4 + a*x^2}{2 + x^2}[/tex]
Now we just need to isolate "a"
[tex]a*(2 + x^2) = 4 + a*x^2[/tex]
[tex]2*a + a*x^2 = 4 + a*x^2[/tex]
Now we can subtract a*x^2 in both sides to get:
[tex]2*a = 4\\a = 4/2 = 2[/tex]
Then the solution is:
[tex]y = \sqrt{4 + 2*x^2}[/tex]
The correct option is option a.
