Jika diketahui besar sudut ABD = 5×°, dan sudut BDC = 2×°, dan sudut ATD = 30° maka besar sudut BDC=... a. 10° b. 20° c. 25° d. 30°

180- 5x + 2x + 30 = 180
-3x = 180-180-30
-3x = -30
x =10

BDC = 2x = 2 x 10 = 20 derajat :)

B. 20

∠ABD+∠DBT = 180
5x+∠DBT = 180
∠DBT=180-5x
Total sudut segitiga = 180
∠BDT+∠DBT+∠DTB=180
2x-5x+180+30=180
-3x+30=180-180
30=3x
x=10
∠BDT=2x
∠BDT=20