Find an explicit formula for the arithmetic sequence 10,-10,-30,-50,...10,−10,−30,−50,...10, comma, minus, 10, comma, minus, 30, comma, minus, 50, comma, point, point, point. Note: the first term should be \textit{c(1)}c(1)start text, c, left parenthesis, 1, right parenthesis, end text. c(n)=c(n)=c, left parenthesis, n, right parenthesis, equals