# Algebra (Discrete Mathematics)

• Sep 29th 2008, 06:54 PM
kwikness
Algebra (Discrete Mathematics)
Hi.. I'm following along in a book for my Discrete Mathematics class and I'm having trouble finding out what's going on between two steps algebraically.

21-1(77-3 x 21)
= 4 x 21 - 1 x 77

Exactly what is happening between these two steps? I can't see where the 4 comes from.

(Note: The xs in this problem stand for multiplication, not a variable x)

Thank you.
• Sep 29th 2008, 07:00 PM
Jhevon
Quote:

Originally Posted by kwikness
Hi.. I'm following along in a book for my Discrete Mathematics class and I'm having trouble finding out what's going on between two steps algebraically.

21-1(77-3 x 21)
= 4 x 21 - 1 x 77

Exactly what is happening between these two steps? I can't see where the 4 comes from.

(Note: The xs in this problem stand for multiplication, not a variable x)

Thank you.

21 - (77 - 3x21) = 21 - 77 + 3x21 .....by multiplying out so as to expand the brackets

now we have 1 21 in front and 3 21's in the back. together, we hae 4 21's

so we get 4x21 - 77 or 4x21 - 1x77