Algebra Factorisation and Equations

not happy jan · #1 $Old$ November 5th, 2008, 11:47 PM

Please help!!! 2 questions.
Factorise b^2 -16 and Solve for x: (x+1)(x-4)=0
Can you please show me how to work these out and also show the answer.

thisisme · #2 $Old$ November 5th, 2008, 11:56 PM

Either x+1=0 or x-4=0. Solve these to get x=-1 and x=4.

$b^2-16=(b-4)(b+4)$

This is obtained from the difference of 2 squares, if you don't know this yet then look it up and learn it.

not happy jan · #3 $Old$ November 6th, 2008, 12:16 AM

I understand the factorisation but am having trouble with other one. My daughter seems to think you have to get rid of one of the x's somehow...

thisisme · #4 $Old$ November 6th, 2008, 01:55 AM

No, it is a quadratic which means it has 2 solutions.
You can divide through by x+1 or by x-4 to get either x+1=0 or x-4=0. Thus x=-1 or x=4.