Question

i) +2r2-3x+21, if x = 1+2i.​

Answer 1

Answer:

x3+2x2−3x+21 if x=1+2i

(x−1)2=(2i)2

x2−2x+1=−4

x2−2x+5=0

∴x3+2x2−3x+21

=x(x2−2x+5)+4x2−8x+21

=0+4x2−8x+21

=4(x2−2x+5)+1

=0+1

=1

Value is 1.