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I don't understand how to do this problems: Solve for the variable r, C=2PIr (PI is the pi symbol thing then r is next to it) and this problem solve for the variable l, S=B+1/2Pl please help :)

When you solve for a variable, you want that "letter" on one side and everything else on the other. If we have C = 2*pi*r, then
r = C/(2*pi)

I don't get your second equation. Is that 1/2*P or 1/2*P*I. If the latter than I = .....just as I did the first one.

1) C=2plr so r = C/2pl

2)S=B+1/2Pl so 1 = 2pi(S-B)

thank you for the help! :) but for the second equation it's one half right beside a capital P then a lower case l i do not understand how to solve it

Do you understand what I did for the first one?
C = 2*pi*r
Divide both sides by 2*pi so it is
C/2*pi = 2*pi*r/2*pi
On the right side, now, the 2*pi cancels leaving just r; therefore.
C/(2*pi) = r.

For the second one, my l on the computer looks like the letter 1 so I will make it a capital I.
We have S = B + (1/2)PI
since is is easier to handle numbers rather than fractions, we multiply everyting by 2.
2*S = 2*B + 2*(1/2)*PI
on the right side the 2(1/2) = 1 and the equation is now
2S = 2B + PI
Next, let's subtract 2B from both sides.
2S - 2B = 2B -2B + PI
The 2B on the right side adds out so we are left with
2S - 2B = PI. We have effectively just moved the 2B from the right side to the left side.
Now we solve for I. Probably you can do the rest. Post your work if you want us to check it. But if you don't understand any of the other steps, repost and explain exactly what you don't understand.

To slove for somthing is to get it all by itself on one side of the = sign.

Do the same thing to both sides of the equal sign so the equation stays true.

For example: solve for A, A+B=C
to get A by itself, do A+B-B=C-B
when you do the math A=C-B is the result.

In your first question, you need to move the 2Pi to the other side by deviding both sides by 2Pi.

do the math, and,

the second question, do you mean
solve for I? As in S=B+(1/2P)I ?

or did you mean solve for Pi? S=B+(1/2Pi)?

How did the symbol for pi come about

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