Thread: Finding zeroes for trig functions

When you have functions like these:

y=sinx+cos2x
or
y=-sinx-4cos2x

How can I determine the zeroes? Is there an identity for cos2x that could be useful in factoring a term out, or etc?

Originally Posted by theowne

When you have functions like these:

y=sinx+cos2x
or
y=-sinx-4cos2x

How can I determine the zeroes? Is there an identity for cos2x that could be useful in factoring a term out, or etc?

write as . then your equations break down into quadratic equations in . It is easy to find the zeros from there