Answer:
x=5
Step-by-step explanation:
An isosceles trapezoid has two pairs of congruent base angles. This means angle F has to equal angle E. So we have 2x^2+21=3x^2-4. Move the variables to one side and we get 25=x^2. Square root both sides and we get two values x=5 and x=-5. Since angles cannot necessarily be negative, we only want the positive value. In this case x=5.
