FP1 Calculus URGENT HELP please!

Q3 is from FP1 Calculus...have no idea how to do it since I got two 'problem values' here

Need help please!!!

Integrate as normal. When it comes to substituting limits, you cannot substitute $\infty$ because it is not a number. Instead, you assign a different variable, such as $a$, and take the limit of the integral as $a\rightarrow \infty$

But how about 0? Cuz my teacher also said that we need to replace 0 with a different variable.... that's why I'm confused cuz it then will be two variables😂
Or is it in this case we don't need to consider 0?

Well technically speaking the function $\frac{1}{\sqrt{x}}$ is undefined at x=0 so you would need to replace it as well, but personally I would skip this because the integrated function will be defined at x=0.

If it was $\displaystyle \int_0^{\infty} x^{-3/2}$ or something then you would indeed need to replace the 0.

I've only just finished learning FP1, and this is how I would go about it Replace the infinity with 'a', then integrate as normal. As 'a' tends towards infinity, the integral also tends towards infinity! As I said I'm also just a student so let me know if anyone disagrees