Divas paralēlas taisnes $$a$$ un $$b$$ krusto trešā taisne $$c$$.
($a\parallel b$)

Ja divas paralēlas taisnes krusto trešā taisne:

Kāpšļu leņķi ir vienādi:
$\begin{array}{l}\sphericalangle 1\phantom{\rule{0.147em}{0ex}}\phantom{\rule{0.147em}{0ex}}=\phantom{\rule{0.147em}{0ex}}\sphericalangle 5\\ \sphericalangle 2\phantom{\rule{0.147em}{0ex}}\phantom{\rule{0.147em}{0ex}}=\phantom{\rule{0.147em}{0ex}}\sphericalangle 6\\ \sphericalangle 3\phantom{\rule{0.147em}{0ex}}\phantom{\rule{0.147em}{0ex}}=\phantom{\rule{0.147em}{0ex}}\sphericalangle 7\\ \sphericalangle 4\phantom{\rule{0.147em}{0ex}}\phantom{\rule{0.147em}{0ex}}=\phantom{\rule{0.147em}{0ex}}\sphericalangle 8\end{array}$

Iekšējie šķērsleņķi ir vienādi:
$\begin{array}{l}\sphericalangle 2\phantom{\rule{0.147em}{0ex}}\phantom{\rule{0.147em}{0ex}}=\phantom{\rule{0.147em}{0ex}}\sphericalangle 7\\ \sphericalangle 4\phantom{\rule{0.147em}{0ex}}\phantom{\rule{0.147em}{0ex}}=\phantom{\rule{0.147em}{0ex}}\sphericalangle 5\end{array}$

Iekšējo vienpusleņķu summa ir $180\mathrm{°}$
$\begin{array}{l}\sphericalangle 2\phantom{\rule{0.147em}{0ex}}\phantom{\rule{0.147em}{0ex}}+\phantom{\rule{0.147em}{0ex}}\sphericalangle 5\phantom{\rule{0.147em}{0ex}}\phantom{\rule{0.147em}{0ex}}=180\mathrm{°}\\ \sphericalangle 4\phantom{\rule{0.147em}{0ex}}\phantom{\rule{0.147em}{0ex}}+\phantom{\rule{0.147em}{0ex}}\sphericalangle 7\phantom{\rule{0.147em}{0ex}}=180\mathrm{°}\end{array}$

Atsauce:
Matemātika 7.klasei/Ilze France, Gunta Lāce, Ligita Pickaine, Anita Miķelsone. - Lielvārde: Lielvārds, 2007. - 248 lpp.- izmantotā literatūra: 229. lpp.