In my notes the following formulas are rearranged for the value you are looking for. Can someone tell me why the 2nd formula wouldn't follow the same "algebra manipulation" as the first? Aren't they basically the same?

SPI=EV/PV to EV=SPI*PV.
??? CPI=EV/AC is AC=EV/CPI why isn't this AC*CPI=EV

Thanks for the help.