Answer:
21 - i
Step-by-step explanation:
( 5+i ) * ( 4-i ) = 5 * ( 4-i ) + i *( 4-i )
= 5*4 - 5*i + i*4 - i*i
= 20 - 5i + 4i - i²
= 20 - 5i +4i - (-1) { i² = -1 }
= 20 - 5i +4i + 1
= 21 - i
