Prove that δabc and δedc are similar.

the blanked out numbers are 15 and 12

a) ∠dce is congruent to ∠bca by the vertical angles theorem and 15 over 5 equals 12 over 4 shows the corresponding sides are proportional; therefore, δabc ~ δedc by the sas similarity postulate.

b)∠dce is congruent to ∠cba by the vertical angles theorem and 15 over 5 equals 12 over 4 shows the corresponding sides are proportional; therefore, δabc ~ δedc by the sss similarity postulate.