Because there are 4 inside angles the sum of the four angles must equal 360 degrees.
Add the angles to equal 360:
4x + 3x + 2x + 3x = 360
Simplify:
12x = 360
Solve for x by dividing both sides by 12:
x = 360 /12
x = 30
Now you have x, solve for each angle:
ABC = 4x = 4 x 30 = 120 degrees.
BCD = 3x = 3 x 30 = 90 degrees.
CDA = 2x = 2x 30 = 60 degrees.
DAB = 3x = 3 x 30 = 90 degrees.
C. It's important to know that a four sides figure needs the inside angles when added together need to equal 360 degrees.
(6x-1)+20+(x+14)=180
6x-1+20+x+14=180
6x+x+20+14-1=180
7x+33=180
-33 -33
7x=147
7/7x=147/7
x=21
Measure of angle A=:
(6x-1)
6x-1
6(21)-1
126-1
125
Measure of angle A is 125°
Measure of angle C=
(x+14)
x+14
21+14
35
Measure of angle C is 35°
Because ABCD is an isosceles trapezoid, the angles A and D are congruent.
BA and CD are congruent (given) and AD is congruent to itself (reflexive property).
Then triangles BAD and CDA form a pair of SAS triangles, so they are congruent.
BD and CA are corresponding parts in those triangles, so they are congruent (CPCTC).
