perhatikan gambar belah ketupat ABCD sudut A :sudut B =2:3.besar sudut D.

<A = <C
<B = <D

<A + <B + <C + <D = 360°
2x + 3x + 2x + 3x = 360°
10x = 360
x = 36°

<C = 2x
=2(36)
= 72°