Solution:
(a):
z4=24i−7
Put z=x+iy
⇒(x+iy)4=24i−7⇒[(x+iy)2]2=24i−7⇒[x2+i2y2+2ixy]2=24i−7⇒[(x2−y2)+2ixy]2=24i−7⇒[(x2−y2)2+(2ixy)2+2(x2−y2)(2ixy)]=24i−7⇒(x4+y4−2x2y2)−4x2y2+4ix3y−4ixy3=24i−7⇒x4+y4−6x2y2+i(4x3y−4xy3)=24i−7
On comparing both sides,
x4+y4−6x2y2=−7, 4x3y−4xy3=24⇒(x2−y2)2−(2xy)2=−7, 4xy(x2−y2)=24⇒(x2−y2)2−(2xy)2=−7 ...(i), (x2−y2)=xy6 ...(ii)
Put (ii) in (i),
⇒(xy6)2−(2xy)2=−7⇒x2y236−4x2y2=−7
Put x2y2=t
⇒t36−4t=−7
⇒t=−49,t=4⇒x2y2=−49,x2y2=4
Rejecting negative value as it is impossible for real numbers.
⇒xy=±2⇒x=y±2 ...(iii)
Put (iii) in (ii)
(y24−y2)=±26=±3⇒y24−y2=3;y24−y2=−3⇒y=−4,1;y=−1,4⇒y=±4,±1
Put this in (iii),
x=±21,±2
Thus, solution is z=±21±4i;z=±2±1i
(b):
z2+z−2=i
Put z=x+iy
⇒(x+iy)2+(x+iy)−2=i⇒x2−y2+2ixy+x+iy−2=i⇒(x2−y2+x−2)+i(2xy)=0+i
On comparing,
x2−y2+x−2=0; 2xy=1⇒x2−y2+x−2=0 ...(i); y=2x1 ...(ii)
Put (ii) in (i),
⇒x2−(2x1)2+x−2=0⇒4x4−1+4x3−8x2=0⇒4x4+4x3−8x2−1=0⇒x≈1.07,x≈−2.02
Put these in (ii)
y=0.47,y=−0.25
Thus, solutions are z=1.07+0.47i; z=−2.02−0.25i
(c):
z6=(1+z)6⇒(1+zz)6=1⇒1+zz=1⇒1+zz=eikπ/3 , where k=1,2,..,6
⇒z=1−eikπ/3eikπ/3
Simplify this using trigonometric form and double angle identites to get:
z=−21+icot(6kπ)
Putting k=1,2,...,6
z=−21+icot(6π);−21+icot(3π);−21+icot(2π);−21+icot(32π);−21+icot(65π);−21+icot(π)
z=−21+i3;−21+i(31);−21+i(0);−21+i(−31);−21+i(−3);−21+i(∞)
Thus, solutions are:
z=−21+i3;−21+i(31);−21;−21−i(31);−21−i(3);not defined
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