Subject: name of shape
Name: valentina
Who are you: Student

I have a shape of 4 sides 3 are the same length (2cm each) and the other smaller (1.5cm)

Valentina,

I doubt if there would be a special name because your figure has no special properties. A four-sided figure is called a quadrilateral or quadrangle, whichever name you prefer. There are special names when two of the sides are parallel -- in America the figure is an isosceles trapezoid if two equal sides are not parallel while the other sides are; if no sides are parallel it is a trapezium. (In British English the meanings of the words trapezoid and trapezium are reversed!) (Your figure could not have two of the equal sides parallel because then it would be a parallelogram and opposite sides would necessarily have the same length.)

Chris