Question

solve x² +20 ix +21=0​

Answer 1

x²+20 ix +21=0

or, x²+2.x.10i+(10i)²-(10i)²+21=0

or, (x+10i)²-100i²+21=0

or, (x+10i)²-100×(-1)+21=0

or, (x+10i)²+100+21=0

or, , (x+10i)²+121=0

or, (x+10i)²-121 i² =0

or, (x+10i)²-(11i)² =0

or, (x+10i+11i), (x+10i-11i) = 0

or, (x+21i)(x-i) = 0

so, x = -21i and i Ans.