Intr-un paralelogram <A=<C si <B=<D=>
Daca <A+<B+<C+<D=360
=> <A+<B=180
a) <A=3*<B => 3*<B+B=4*<B=180=> <B=45 =<D, iar <A=3*45=135=<C
b)<A=5*<D
<A+<D=180
5*<D+<D=6*<D=180=> <D=30=<B => <A=5*30=150=<C
c)<B=2/3*<A=> 3*<B=2*<A
2*<A+2*<B=360
3*<B+2*<B=5*<B=360
=> <B=72 =<D =>
<A=180-72=108=<C