geometry
posted by josh .
Given quadrilateral ABCD, with A = 4x  57 and C = x + 3, what value of x ensures that ABCD is a parallelogram?

recall the properties of parallelogram,,
one of the properties of a parallelogram is that the opposite angles are congruent/equal,, since you are given angles A and C, and they are opposite, equate them to get x:
4x  57 = x + 3
combining similar terms,
4x  x = 57 + 3
*when transposing terms to other side of equation, the sign becomes the opposite,, that's why x (from right side) when transposed to left side becomes x, and 57 becomes 57 after transposing,, simplifying this,
3x = 60
x = 20
hope this helps. :)