ITMC 2018 Grade 11 National Preliminary set01 Question 1

Question 1

Printed positive marks are preserved per question. The source uses different blank-answer and incorrect-answer rules by section, including an optional bonus penalty; the import does not reproduce that complete official scoring scheme.

Which function is a decreasing exponential function? The source prints the label D twice; the fifth option is identified as E here.

$f_1(x)=(1/x)^{13}$, $x\ne0$
$f_2(x)=0^x$, $x\ne0$
$f_3(x)=1^{2x}$, $x\in\mathbb R$
$f_4(x)=(\sqrt3-\sqrt2)^{-x}$, $x\in\mathbb R$
$f_5(x)=(\log_2 3)^{-x}$, $x\in\mathbb R$