# math (trig)

posted by .

how do you solve for x?

2cos^24x-1=0

• math (trig) -

First find the cos of 24
multiply this by 2
add 1 to the other side
Finally, divide that answer with 1
and... u have the answer!!! whatever that is...

• math (trig) -

2cos^2 (4x) - 1 = 0
so cos^2 (4x) = 1/2
cos 4x = ±1/√2

so 4x must be an angle in each of the 4 quadrants.
but I know cos 45º = 1/√2
so 4x = 45 or 4x = 135 or 4x = 225 or 4x = 315
then
x = 11.25 or x = 33.75 or x=56.25 or x=78.75

the period of cos 4x = 90º
e.g. 33.75 + 90 = 123.75 would be another possible answer

proof:
LS
= 2 cos^2 (4*123.75) - 1
= 2cos^2 (495) - 1
= 2(1/2) - 1
= 0 = RS

• math (trig) -

just follow my way, its much simpler

• math (trig) -

MC, except you don't get the right answer, lol

• math (trig) -

prove it Reiny
:)
my way always works

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