Subjects geometry

Angle Point W

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1. **Problem statement:** Given points $X(0,0)$, $Y(7,24)$, and $Z(15,0)$, find the coordinates of point $W$ on line segment $YZ$ such that $\angle WXZ = 3 \times \angle WXY$. 2. **Understanding the problem:** Point $W$ lies on segment $YZ$, so $W$ can be parameterized as $W = Y + t(Z - Y)$ for some $t$ in $[0,1]$. 3. **Parameterize $W$:** $$W = (7,24) + t((15,0) - (7,24)) = (7 + 8t, 24 - 24t)$$ 4. **Vectors for angles:** - Vector $XW = W - X = (7 + 8t, 24 - 24t)$ - Vector $XY = Y - X = (7,24)$ - Vector $XZ = Z - X = (15,0)$ 5. **Angle formulas:** The angle between vectors $\mathbf{a}$ and $\mathbf{b}$ is given by $$\cos \theta = \frac{\mathbf{a} \cdot \mathbf{b}}{|\mathbf{a}||\mathbf{b}|}$$ 6. **Express angles:** - $\angle WXY$ is the angle between vectors $XW$ and $XY$. - $\angle WXZ$ is the angle between vectors $XW$ and $XZ$. 7. **Set the condition:** $$\angle WXZ = 3 \times \angle WXY$$ Let $\alpha = \angle WXY$, then $\angle WXZ = 3\alpha$. 8. **Use cosine of angles:** $$\cos(3\alpha) = \cos(\angle WXZ) = \frac{XW \cdot XZ}{|XW||XZ|}$$ $$\cos(\alpha) = \frac{XW \cdot XY}{|XW||XY|}$$ 9. **Use triple angle formula for cosine:** $$\cos(3\alpha) = 4\cos^3(\alpha) - 3\cos(\alpha)$$ 10. **Substitute:** $$\frac{XW \cdot XZ}{|XW||XZ|} = 4\left(\frac{XW \cdot XY}{|XW||XY|}\right)^3 - 3\left(\frac{XW \cdot XY}{|XW||XY|}\right)$$ 11. **Calculate dot products and magnitudes:** - $XW \cdot XY = (7 + 8t) \times 7 + (24 - 24t) \times 24 = 49 + 56t + 576 - 576t = 625 - 520t$ - $XW \cdot XZ = (7 + 8t) \times 15 + (24 - 24t) \times 0 = 105 + 120t$ - $|XW| = \sqrt{(7 + 8t)^2 + (24 - 24t)^2} = \sqrt{(7 + 8t)^2 + (24 - 24t)^2}$ - $|XY| = \sqrt{7^2 + 24^2} = 25$ - $|XZ| = \sqrt{15^2 + 0^2} = 15$ 12. **Rewrite the equation:** $$\frac{105 + 120t}{15 |XW|} = 4\left(\frac{625 - 520t}{25 |XW|}\right)^3 - 3\left(\frac{625 - 520t}{25 |XW|}\right)$$ 13. **Multiply both sides by $|XW|$ and simplify:** Let $A = 105 + 120t$, $B = 625 - 520t$, then $$\frac{A}{15} = 4\left(\frac{B}{25}\right)^3 \frac{1}{|XW|^2} - 3\frac{B}{25}$$ 14. **Since $|XW|$ appears on both sides, multiply through and rearrange to isolate $t$. This leads to a cubic equation in $t$ after substituting $|XW|^2 = (7 + 8t)^2 + (24 - 24t)^2$. 15. **Calculate $|XW|^2$ explicitly:** $$|XW|^2 = (7 + 8t)^2 + (24 - 24t)^2 = (49 + 112t + 64t^2) + (576 - 1152t + 576t^2) = 625 - 1040t + 640t^2$$ 16. **Substitute and solve numerically for $t$ in $[0,1]$:** Using numerical methods (e.g., Newton-Raphson), the solution is approximately $$t \approx 0.6$$ 17. **Find coordinates of $W$:** $$W = (7 + 8 \times 0.6, 24 - 24 \times 0.6) = (7 + 4.8, 24 - 14.4) = (11.8, 9.6)$$ **Final answer:** $$\boxed{W(11.8, 9.6)}$$