Answer:
3.) 90°; perpendicular bisector; AB; 9; E, AB.
Explanation:
∠BEC and ∠BED form a linear pair. This means their sum is 180°. Since we know that m∠BEC = 90°, this means that
m∠BED = 180-90 = 90°.
Since AE = AB and CD intersects AB at right angles, this means that CD is the perpendicular bisector of AB.
This means that AE = 1/2AB.
If AB = 18, then AE = 1/2(18) = 9.