I need help simplifying this trig. expression, please?

Question

cosC - 2sinCcosC / cos^2C - sin^2C + sinC - 1

Answer 1

You need to use parentheses when transposing to yahoo answers single line format. The expression should look like this:
(cosC - 2sinCcosC)/(cos^2C -sin^2C + sinC -1)
Substitute 1 - sin^2C for cos^2C:
= cosC(1 - 2sinC)/[(1 - sin^2C) - sin^2C + sinC -1]
= cosC(1 - 2sinC)/(sinC - 2sin^2C)
= cosC(1 - 2sinC)/sinC(1 - 2sinC)
= cotC