Do you want a general solution or from 0 <= x < 2pi?
tan^2(2x) - 1 = 0
tan^2(2x) = 1
Take the square root of both sides,
tan(2x) = +/- 1
Two equations:
tan(2x) = 1
tan(2x) = -1
Solve each equation.
tan(2x) = 1, 2x = {pi/4, 5pi/4, 9pi/4, 13pi/4},
x = { pi/8, 5pi/8, 9pi/8, 13pi/8 }
tan(2x) = -1, 2x = { 3pi/4, 7pi/4, 11pi/4, 15pi/4 },
x = { 3pi/8, 7pi/8, 11pi/8, 15pi/8}
So for solutions within [0, 2pi),
x = {pi/8, 3pi/8, 5pi/8, 7pi/8, 9pi/8, 11pi/8, 13pi/8, 15pi/8 }
$ 2000 is invested at 3 % interest and $ 4000 is invested at 8 % interest
<em><u>Solution:</u></em>
Given that, total of $6000 was invested
Let "x" be the amount invested at 3 % interest
Then, (6000 - x) is the amount invested at 8 % interest
Given that,
<em><u>The total yearly interest amounted to $380</u></em>
Then, we can frame a equation as:

<em><u>Solve the above expression for "x"</u></em>

Thus, $ 2000 is invested at 3 % interest
(6000 - x) = 6000 - 2000 = 4000
$ 4000 is invested at 8 % interest
Get the mixed number into one fraction

Get a common denominator

Now add

You can get it back to a mixed number
[[x]] means to round down to the greatest integer less than or equal to x.