If you're seeing this message, it means we're having trouble loading external resources on our website.

If you're behind a web filter, please make sure that the domains *.kastatic.org and *.kasandbox.org are unblocked.

Main content

# Solving an equation for a variable

## Video transcript

solve P equals 2l plus 2w for L so this right here this is just a formula for the perimeter of a rectangle perimeter is equal to two times the length plus two times the width but they just want us to solve this equation right here solve for L so let's do that so we have P is equal to two times two times L plus 2 times W so we need to solve for L so let's isolate all of the L terms on one side and the best way we could we could just do that by leaving it here on the right and then getting rid of this 2w and the best way to get rid of the 2w is to subtract it from the right but if you're going to subtract it from the right you also have to subtract it from the left if you want this equality to hold so you have to also subtract it from the left and so the left-hand side becomes P minus 2w P minus 2w and the right-hand side you get this 2w minus 2w cancels out you just have a 2l and then if you want to solve for L you just have to divide both sides of this equation by 2 you just divide both sides of this equation by 2 and we have isolated our L we get L is equal to P minus 2w over 2 or if we wanted to write it the other way we could write L is equal to P minus 2w over 2 and we are done