Browse Questions

# The real value of $' a '$ for which $\;3i^{3}-2ai^{2}+(1-a)i+5\;$ is real is

$(a)\;-2\qquad(b)\;\pm6\qquad(c)\;\pm3\qquad(d)\;4$

Answer : $-\;2$
Explanation :
$\;3i^{3}-2ai^{2}+(1-a)i+5\; =-3i+2a+5+(1-a)i$
$=2a+5+i(-a-2)\;$, which is real
If $\;-a-2 =0\; i .e \;a=-2$