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Besar ∠BDC
= 180 - (8x - 11)
= 180 - 8x + 11
= (191 - 8x)°

Besar ∠CBD
= 180 - 38 - (191 - 8x)
= 180 - 38 - 191 + 8x
= (-49 + 8x)°

∠ABD + ∠CBD = 180 (berpelurus)
(9x + 25) + (-49 + 8x) = 180
9x + 25 - 49 + 8x = 180
17x - 24 = 180
17x = 204
x = 204/17
x = 12°

Besar ∠CBD
= -49 + 8x
= -49 + 8 (12)
= -49 + 96
= 47°

atau

Besar ∠CBD
= 180 - (9x + 25)
= 180 - 9x - 25
= -9x + 155
= -9 (12) + 155
= -108 + 155
= 47°