$-53$

$-57$

Question $28$

Write the general term for the geometric sequence $40,20,10,5dots{a}_n=a_1$

$a_n=40(\frac{1}{2}{)}^{n-1}$

$a_n=40(2{)}^{n-1}$

$a_n=40(-\frac{1}{2}{)}^{n-1}$

$a_n=40(-2{)}^{n-1}$