besar sudut CBD adalah…

➡sudut garis lurus = sudut ∆ = 180°

Maka :

x + 9 + 30 + ABC = 180°

ABC = 180 - 39 - x
ABC = 141 - x................ (1)

➡CBD = 2x + 3, maka :

CBD + ABC = 180
2x + 3 + 141 - x = 180
x = 180 - 144
x = 36°

Sehingga sudut CBD :
= 2x + 3
= 2(36) + 3
= 72 + 3
= 75°