Respuesta :

gmany
Look at the picture.


[tex]\Delta ADC\ and\ \Delta CDB\ are\ similar\ therefore\\\\\dfrac{y}{4}=\dfrac{9}{y}\ \ \ \ |cross\ multiply\\\\y\cdot y=4\cdot9\\\\y^2=36\to y=\sqrt{36}\to y=6[/tex]
Ver imagen gmany