The textbook says :

MR = P[1-(1/E)] (when E is price elasticity.)

However, I cannot understand the equation.

As MR=P+Q(△P/△Q) and E=(P/Q)(△Q/△P), isn’t it the correct equation that MR=P[1+(1/E)], not MR = P[1-(1/E)]?

The textbook says :

MR = P[1-(1/E)] (when E is price elasticity.)

However, I cannot understand the equation.

As MR=P+Q(△P/△Q) and E=(P/Q)(△Q/△P), isn’t it the correct equation that MR=P[1+(1/E)], not MR = P[1-(1/E)]?