Two negative signs together change the sign to a positive sign.
Using the distributive property with the 7 you would have -(-7), the two negatives would make it +7
So you end up with -8 + 7
Circumference of the smaller circle, using

, is approximately equal to 18.85 (I used the high floating point precision approximation of pi my calculator has in memory, then rounded to 2 decimal points.)
Using the formula

, which in English says "the smaller circle's circumference is equal to 20% of the larger circle's", we can substitute the known value S:

and solve for L:

.
So the larger circle has a circumference approximately equal to 92.5 units.
Vertex Form of Quadratic Equation - MathBitsNotebook(A1 - CCSS Math) f (x) = a(x - h)2 + k, where (h, k) is the vertex of the parabola. FYI: Different textbooks have different interpretations of the reference "standard form" of a quadratic function...:)
7/x = 5/y
Can be changed to:
5x = 7y
So, x = (7/5)y and
y = (5/7)x