נתון ( ∙ {\displaystyle \bullet } ): ◻ A B C D D E = B E B C = 4 c m D C = 9 c m {\displaystyle {\begin{aligned}&\square ABCD\\&DE=BE\\&BC=4_{cm}\\&DC=9_{cm}\end{aligned}}}
צ.ל : ∠ E B C K E = ? {\displaystyle {\begin{aligned}&\angle EBC\\&KE=?\end{aligned}}}
הוכחה : △ A B C tan ∠ = 4 9 ∠ D = α = 23.962 B E = D E ∙ ∠ B D C = ∠ E B D = 23.962 △ B D C ∠ E B C = 90 − 23.962 = 42.076 ◼ B E = cos 42.08 = 4 B E 0.742 B E = 4 / : 0.742 B E = 5.389 K E = sin 23.962 = K E 5.389 K E = 2.188 {\displaystyle {\begin{aligned}&\triangle ABC\\&\tan \angle ={\frac {4}{9}}\\&\angle D=\alpha =23.962\\&BE=DE\bullet \\&\angle BDC=\angle EBD=23.962\\&\triangle BDC\\&\angle EBC=90-23.962=42.076\blacksquare \\&BE=\cos 42.08={\frac {4}{BE}}\\&0.742BE=4/:0.742\\&BE=5.389\\&KE=\sin 23.962={\frac {KE}{5.389}}\\&KE=2.188\\\end{aligned}}}
