ini bagaimana? dgn caranya yaa, terimakasih

Diketahui :
<ABD = (4x + 20)°
<CDE = (4x - 5)°
<BCD = 35°

Ditanya : <BDC ??

Penyelesaian :
Ingat !
(i) <BDC & <CDE saling berpelurus,maka :
<BDC = 180° - (4x - 5)°

(ii) <CBD & <ABD saling berpelurus,maka :
<CBD = 180° - (4x + 20)°

(iii) <CBD + <BDC + <BCD (sudut sudut dalam segitiga) = 180°

Jawab:
'Tentukan Nilai x'
<CBD + <BDC + <BCD = 180°
→ 180°-(4x+20)° + 180°-(4x-5)° + 35° = 180°
→ -(4x+20)° -(4x-5)° + 395° = 180°
→ -4x - 20 -4x + 5 = 180° - 395°
→ -8x - 15 = -215°
→ -8x = -215° + 15°
→ -8x = -200
→ x = -200 / -8
→ x = 25°

Jadi, besar <BDC ?
→ <BDC = 180° - (4x - 5)°
→ <BDC = 180° - (4 . 25 - 5)°
→ <BDC = 180° - (100 - 5)°
→ <BDC = 180° - 95°
→ <BDC = 85° (C)