How do you multiply #(2r^2+5r-1)(5r^2+2r-8)#?

1 Answer
Jun 28, 2018

Answer:

#10r^4+29r^3-11r^2-42r+8#

Explanation:

#"each term in the second factor is multiplied by each term"#
#"in the first factor"#

#=(color(red)(2r^2+5r-1))(5r^2+2r-8)#

#=color(red)(2r^2)(5r^2+2r-8)color(red)(+5r)(5r^2+2r-8)#
#color(white)(=)color(red)(-1)(5r^2+2r-8)#

#"distributing gives"#

#=10r^4+4r^3-16r^2+25r^3+10r^2-40r-5r^2-2r+8#

#"collecting like terms"#

#=10r^4+29r^3-11r^2-42r+8#