if x+y+z =1. then xy+yz+zx is	Choose one:  A) 1/2  B) 1/3  C) 1/4  D) 1/5  E) 1/6
1/2+1/2+0= 
<gadget id="calculator">1/2+1/2+0</gadget>
<output>1</output>
1   xy=1/2*1/2=1/4   ANSWER:1/4
<result>C</result>
if x+y+z =1. then xy+yz+zx is