Answer :
One equivalent is [tex]A=h( \frac{ b_{1}+b_{2} }{2}) [/tex]
Another example is [tex]A= \frac{(b_{1}+b_{2})(h)}{2} [/tex]
Another example is [tex]A= \frac{(b_{1}+b_{2})(h)}{2} [/tex]