Question

Problem is in the attachment.

Answer 1

Putting in
\[ f(x+h) = (x+h)^2+3 \]
into the expression results in
\[ \frac{f(x+h)-f(x)}{h} = \frac{(x+h)^2+3-(x^2+3)}{h} = \\
\frac{(x^2+2xh+h^2)+3-x^2-3}{h} = \frac{2xh+h^2}{h} = 2x+h \]

Answer 2

Thank you!