Question

Can somebody help me????

Answer 1

$f(x)=5x^2-3\\\\\\ f(x+a)=5(x+a)^2-3=5(x^2+2ax+a^2)-3=\\\\=\boxed{5x^2+10ax+5a^2-3}$

On the other hand:

$f(x+a)=5x^2+30x+42$

so:

$10ax=30x\\\\10a=30\qquad|:10\\\\\boxed{a=3}$

Answer C.