panjang AD adalah...

AC = √144+81 = 15 cm
AD =√225+64 = 17 cm
semoga membantu

cari AC dulu:
[tex] = \sqrt{ {12}^{2} + {9}^{2} } \\ = \sqrt{144 + 81} \\ = \sqrt{225} \\ = 15[/tex]
lalu cari AD:
[tex] = \sqrt{ {15}^{2} + {8}^{2} } \\ = \sqrt{225 + 64} \\ = \sqrt{289} \\ = 17[/tex]
jawabannya B. 17 cm