Given,
The complex number z=x+iy be such that 2z+i2z−3i is purely imaginary,
Now putting the value of z=x+iy in 2z+i2z−3i we get,
2(x+iy)+i2(x+iy)−3i=(2x+i(2y+1))(2x+i(2y−3))(2x−i(2y+1))(2x−i(2y+1))
Now taking real part as,
4x2+(2y+1)24x2+(2y−3)(2y+1)=0
⇒4x2+4y2−4y−3=0
⇒x2+y2−y−43=0
Now using,
x+y2=0⇒x=−y2 we get,
x2+y2−y−43=0
⇒y4+y2−y−43=0
⇒y4+y2−y=43