Complex Numbers

 

Express (4 - 5i)(5 + 5i) in the form a + bi, where a and b are integers and i^2 = -1.   

 

Just multiply it out, then combine like terms.  

 

(4 - 5i)(5 + 5i)  =  20 + 20i – 25i – 25i²   ( remember since i² is –1 then –25i² becomes +25 )  

 

                            20 – 5i + 25   

 

                            45 – 5i  

^.