Expressing the Area of a Shape with a Letter

For the six figures Square, Rectangle, Triangles, Trapezoid, Rhombus and Parallelogram, one side or one diagonal is set as x, the tie with the area y is written as an expression, and both directions, x to y and y to x, are found, as Calculation. The drawings carry a fixed length and x written in.

The Trapezoid alone has two fixed figures in the drawing, and the bottom side added to x changes places with the height multiplied afterward. The figure joined to x by addition in the expression set up has to be the length of the side facing x on the drawing.

The run of three questions to a set is inherited from Relational Expressions and Substitution. What has grown is the shape of the expressions, which now carry a division by 2 or parentheses, and the labor of reading which length on the drawing is fixed.