Answer:
If AB and CD are perpendicular, (slope of AB) x (slope of CD) = -1
9/a = -1
a = -9
-9
Step-by-step explanation:
flip and change the sign of [tex]\frac{3}{4}[/tex]
[tex]\frac{4}{-3}[/tex]
set equal to each other
[tex]\frac{4}{-3}[/tex] = [tex]\frac{12}{a}[/tex]
cross multiply
4a = -36
divide by 4
