The length of AD in parallelogram ABCD is: 23 units.
What is a Parallelogram?
A parallelogram is a quadrilateral with two pairs of opposite sides that have congruent lengths.
Thus:
AD = BC
Substitute
x + 21 = 12x - 1
Combine like terms
x - 12x = -21 - 1
-11x = -22
x = 2
AD = x + 21
Plug in the value of x
AD = 2 + 21
AD = 23 units.
Thus, the length of AD in parallelogram ABCD is: 23 units.
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