If fy > 0 and yz < 0, which of the following must be negative:  Pick one:  A) fyz  B) fy(z^2)  C) f(y^2)z  D) x(y^2)(z^2)  E) (x^2)(y^2)(z^2)
fy &gt; 0 means that fy is positive.   yz &lt; 0 means that yz is negative.   f(y^2)z = (fy)(yz) = positive*negative = negative. Thus option f(y^2)z is always negative.
<result>C</result>
If fy > 0 and yz < 0, which of the following must be negative: