Question

Can somebody help me with this​

Answer 1

-9

Explanation:

flip and change the sign of
`(3)/(4)`

`(4)/(-3)`

set equal to each other

`(4)/(-3)` =
`(12)/(a)`

cross multiply

4a = -36

divide by 4

a = -9

Answer 2

If AB and CD are perpendicular, (slope of AB) x (slope of CD) = -1

9/a = -1

a = -9