A team of archaeologists wants to dig for fossils in a triangular area marked by three stakes. The distances between the stakes are shown in the diagram. Which expression represents the dig area in square feet?

squares, rhombus, rectangles

a_n = a_1 + (n - 1)d

the first term is 6.

the common difference d = ?

when you find d, replace n with 7 and d with the common difference to find your answer.

use distributive property on all like terms and change your signs if you have a double negative or if you have positive/negative