parallelograms
<a href="https://scienceres-edcp-educ.sites.olt.ubc.ca/2012/07/27/deriving-the-area-of-triangles/" title="Deriving the Area of Triangles"><img src="https://scienceres-edcp-educ.sites.olt.ubc.ca/files/2012/07/elem_math_shape_areaTriangles-150x150.jpg" alt="Deriving the Area of Triangles" class="thumbnail thumbnail " /></a>