Inverse Trig System
1. **State the problem:**
We are given two equations involving inverse trigonometric functions:
$$\sin^{-1}(\sqrt{x}) = \cos^{-1}(\sqrt{y})$$
and
$$\tan\left(\tan^{-1}(3x) - \tan^{-1}(2y)\right) + \tan\left(\tan^{-1}(3y) - \tan^{-1}(2x)\right) = 1.$$
We need to find the values of $x$ and $y$.
2. **Use the identity relating inverse sine and inverse cosine:**
Recall that for $\theta$ in $[0, \frac{\pi}{2}]$,
$$\sin^{-1}(a) + \cos^{-1}(a) = \frac{\pi}{2}.$$
Since $\sin^{-1}(\sqrt{x}) = \cos^{-1}(\sqrt{y})$, this implies
$$\sin^{-1}(\sqrt{x}) + \cos^{-1}(\sqrt{y}) = \frac{\pi}{2}.$$
Therefore,
$$\sin^{-1}(\sqrt{x}) = \cos^{-1}(\sqrt{y}) = \theta,$$
and
$$\theta + \theta = \frac{\pi}{2} \implies 2\theta = \frac{\pi}{2} \implies \theta = \frac{\pi}{4}.$$
3. **Find $x$ and $y$ from $\theta = \frac{\pi}{4}$:**
Since
$$\sin^{-1}(\sqrt{x}) = \frac{\pi}{4},$$
we have
$$\sqrt{x} = \sin\left(\frac{\pi}{4}\right) = \frac{\sqrt{2}}{2}.$$
Squaring both sides,
$$x = \left(\frac{\sqrt{2}}{2}\right)^2 = \frac{1}{2}.$$
Similarly,
$$\cos^{-1}(\sqrt{y}) = \frac{\pi}{4} \implies \sqrt{y} = \cos\left(\frac{\pi}{4}\right) = \frac{\sqrt{2}}{2}.$$
Squaring,
$$y = \frac{1}{2}.$$
4. **Check the second equation:**
Recall the formula for tangent of difference:
$$\tan(A - B) = \frac{\tan A - \tan B}{1 + \tan A \tan B}.$$
Let
$$A = \tan^{-1}(3x), \quad B = \tan^{-1}(2y),$$
and
$$C = \tan^{-1}(3y), \quad D = \tan^{-1}(2x).$$
Substitute $x = y = \frac{1}{2}$:
$$3x = 3 \times \frac{1}{2} = \frac{3}{2}, \quad 2y = 2 \times \frac{1}{2} = 1,$$
$$3y = \frac{3}{2}, \quad 2x = 1.$$
Calculate each tangent difference:
$$\tan(A - B) = \frac{\frac{3}{2} - 1}{1 + \frac{3}{2} \times 1} = \frac{\frac{1}{2}}{1 + \frac{3}{2}} = \frac{\frac{1}{2}}{\frac{5}{2}} = \frac{1}{5}.$$
Similarly,
$$\tan(C - D) = \frac{\frac{3}{2} - 1}{1 + \frac{3}{2} \times 1} = \frac{1}{5}.$$
Sum these:
$$\frac{1}{5} + \frac{1}{5} = \frac{2}{5} \neq 1.$$
5. **Re-examine the second equation:**
The sum of the two tangent expressions equals 1, but with $x = y = \frac{1}{2}$, it equals $\frac{2}{5}$.
Try to find $x$ and $y$ such that the second equation holds.
6. **Use the tangent subtraction formula for both terms and sum:**
$$\tan(\tan^{-1}(3x) - \tan^{-1}(2y)) = \frac{3x - 2y}{1 + 6xy},$$
$$\tan(\tan^{-1}(3y) - \tan^{-1}(2x)) = \frac{3y - 2x}{1 + 6xy}.$$
Sum:
$$\frac{3x - 2y}{1 + 6xy} + \frac{3y - 2x}{1 + 6xy} = \frac{(3x - 2y) + (3y - 2x)}{1 + 6xy} = \frac{(3x - 2x) + (3y - 2y)}{1 + 6xy} = \frac{x + y}{1 + 6xy}.$$
Set equal to 1:
$$\frac{x + y}{1 + 6xy} = 1 \implies x + y = 1 + 6xy.$$
7. **Recall from step 3 that $x = y = \frac{1}{2}$ satisfies the first equation. Substitute into the above:**
$$\frac{1}{2} + \frac{1}{2} = 1 + 6 \times \frac{1}{2} \times \frac{1}{2} \implies 1 = 1 + \frac{3}{2} = 2.5,$$
which is false.
8. **Solve the system:**
From step 3, $\sqrt{x} = \sin \theta$, $\sqrt{y} = \cos \theta$, and $\theta = \frac{\pi}{4}$.
From step 6, the second equation reduces to
$$x + y = 1 + 6xy.$$
Substitute $y = 1 - x$ (from $x + y = 1 + 6xy$ rearranged):
$$x + y = 1 + 6xy \implies y = 1 + 6xy - x.$$
But this is complicated; instead, use the relation from the first equation:
$$\sqrt{x} = \sin \theta, \quad \sqrt{y} = \cos \theta,$$
so
$$x = \sin^2 \theta, \quad y = \cos^2 \theta.$$
Substitute into the second equation:
$$\sin^2 \theta + \cos^2 \theta = 1 + 6 \sin^2 \theta \cos^2 \theta.$$
Since $\sin^2 \theta + \cos^2 \theta = 1$, this becomes
$$1 = 1 + 6 \sin^2 \theta \cos^2 \theta \implies 6 \sin^2 \theta \cos^2 \theta = 0.$$
9. **Solve for $\theta$:**
$$\sin^2 \theta \cos^2 \theta = 0 \implies \sin \theta = 0 \text{ or } \cos \theta = 0.$$
But $\theta$ must satisfy the first equation $\sin^{-1}(\sqrt{x}) = \cos^{-1}(\sqrt{y}) = \theta$, and $\theta$ is in $[0, \frac{\pi}{2}]$.
If $\sin \theta = 0$, then $\theta = 0$, so
$$x = \sin^2 0 = 0, \quad y = \cos^2 0 = 1.$$
If $\cos \theta = 0$, then $\theta = \frac{\pi}{2}$, so
$$x = \sin^2 \frac{\pi}{2} = 1, \quad y = \cos^2 \frac{\pi}{2} = 0.$$
10. **Check these solutions in the original equations:**
- For $x=0$, $y=1$:
$$\sin^{-1}(\sqrt{0}) = 0, \quad \cos^{-1}(\sqrt{1}) = \cos^{-1}(1) = 0,$$
so first equation holds.
Second equation:
$$\frac{x + y}{1 + 6xy} = \frac{0 + 1}{1 + 0} = 1,$$
which holds.
- For $x=1$, $y=0$:
$$\sin^{-1}(\sqrt{1}) = \sin^{-1}(1) = \frac{\pi}{2}, \quad \cos^{-1}(\sqrt{0}) = \cos^{-1}(0) = \frac{\pi}{2},$$
first equation holds.
Second equation:
$$\frac{1 + 0}{1 + 0} = 1,$$
which holds.
**Final answers:**
$$\boxed{(x,y) = (0,1) \text{ or } (1,0)}.$$