Answer:
- a/b = c/d
- a/c = b/d
- b/a = d/c
- c/a = d/b
Explanation:
The possible proportions can be formed by dividing the equation ...
ad = bc
by any of the four products that consist of one left-side variable and one right-side variable.
Dividing by ab gives ...
d/b = c/a
Dividing by ac gives ...
d/c = b/a
Dividing by bd gives ...
a/b = c/d
And dividing by cd gives ...
a/c = b/d
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Comment on writing proportions
Any proportion can be written in any of these four ways. It is generally convenient to choose the one that has the unknown variable as a numerator with a denominator of 1 (if possible).