So, basically I picked the one direction that doesn't work for the [111] plane. haha
I reworked it with the other two possible slip directions and they both gave the right answer.
Thanks for the reply.
The problem said:
"Determine the magnitude of the Schmid factor for an FCC single crystal oriented with its [100] direction parallel to the loading axis. "
The Schmid factor is the
"cos(\phi)*cos(\lambda)"
term in the equation for resolved shear stress.
I know that the slip planes...