Help Cannot solve a trig. equation

[Cloe]

This is from Heinemann Edexcel C2 book page 153 Ex 10D

solve 4cos^2(x) - 5 sin(x) - 5 = 0 for x between 0 and 360 degrees

[Unregistered]

@ = theta ^2 = squared

Q: 4cos^2 @ - 5 sin@ - 5 = 0

remember:
sin^2@ + cos^2@ = 1

so:
cos^2@ = 1 - sin^2@

4(1 - sin^2@) - 5 sin@ - 5 = 0

Multiply out and factorise:

(4sin@ +1)(sin@ + 1)

4sin@ = -1 and sin@ = -1
sin@ = -1/4 @ = -90
@ = -14.47

Solve for values between 0 and 360 with a sin graph diagram.

:) hope that helps.

I like trying to help people on here, its good reivsion :)

[Cloe]

Thanks whoever u r.