Try: circle area, U = I × R, radius
Proportions, rational expressions, ratios and scaling.
a/b = c/x ⇒ x = bc/a
a/b+c/d = (ad+bc)/(bd)
a/b·c/d = ac/(bd)
(a/b)/(c/d) = ad/(bc)
r = a/b × 100%
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