Posted by **anon** on Monday, October 21, 2013 at 5:36pm.

cos2x-sinx=0. Factor and solve for sinx

- math -
**Reiny**, Monday, October 21, 2013 at 5:43pm
1 - 2sin^2 x - sinx = 0

2sin^2 x + sinx - 1 = 0

(2sinx - 1)(sinx + 1) = 0

sinx = 1/2 or sinx = -1

in degrees, x = 30° , 150° , 270°

in radians, x = π/5 , 5π/6 , 3π/2

- math -
**anon**, Monday, October 21, 2013 at 5:46pm
Thanks. I was wondering, why is it "+ sin x" in the second step?

- math -
**anon**, Monday, October 21, 2013 at 5:47pm
do you just change all the signs of the terms? if so, why is this necessary?

- math -
**Reiny**, Monday, October 21, 2013 at 5:51pm
I multiplied each term by -1

(notice all the signs have switched)

I like my quadratics to start with a positive coefficient, although that would not be necessary.

It just makes it easier to factor.

- math -
**anon**, Monday, October 21, 2013 at 5:55pm
ok thank you.

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