What exactly is r^2 - 49 called and how do you solve it?

I think its called a binomial or something but I'm not that sure.... How do you solve it? Thats just an example show me how to with a different one.What exactly is r^2 - 49 called and how do you solve it?
r^2-49 = (r+7)(r-7)


r = +-7





x^2-64 = (x+8)(x-8)


x = +-8





t^2-81 = (t+9)(t-9)


t = +-9What exactly is r^2 - 49 called and how do you solve it?
First of all it's an expression, not an equation. So you can't ';solve'; it for anything. If you want to FACTOR this, that's another story.





Second of all, yes, it's a binomial (bi + nomial = two terms). And since 49 = 7^2, you can call it ';the difference of two squares';.





In general, a^2 - b^2 = (a+b)(a-b). So here you have (r+7)(r-7).





%26gt;%26gt;I also forgot to mention; what about problems like 4x^2 - 81y^2


%26gt;%26gt;that have two different variables?





Same rules apply. Get it into the form of a^2 - b^2, then rewrite it as (a+b)(a-b).
difference of 2 squares


= (r-7)(r+7)