Question

4x2 +9y2 = 72

Answer 1

Answer:

       $\bold{\left(\dfrac{3}{13}\ ,\ \dfrac{4\sqrt{13}}{13}\right)\qquad\vee\qquad \left(\dfrac{3}{13}\ ,\ -\dfrac{4\sqrt{13}}{13}\right)}$

Step-by-step explanation:

x - y² = -1     ⇒   - y² = - x - 1    ⇒    y² = x + 1   {x≥-1}

4x² + 9y² = 72

4x² + 9(x + 1)² = 72

4x² + 9(x² + 2x + 1) = 72

4x² + 9x² + 18x + 9 - 72 = 0

13x² + 18x - 63 = 0     ⇒   a = 13,  b = 18,  c = -63

$x=\dfrac{-18\pm\sqrt{18^2-4\cdot13\cdot(-63)}}{2\cdot13}=\dfrac{-18\pm\sqrt{324+252}}{26}=\dfrac{-18\pm\sqrt{576}}{26}\\\\x=\dfrac{-18+24}{26}=\dfrac3{13}\qquad\vee\qquad x=\dfrac{-18-24}{26}=-\dfrac{21}{13}\\\\ y^2= x + 1\quad\iff\quad x\ge-1\\\\y^2=\dfrac3{13}+1\\\\ y^2=\dfrac{16}{13}\\\\y=\dfrac{4}{\sqrt{13}}=\dfrac{4\sqrt{13}}{13}\qquad\vee\qquad y=-\dfrac{4\sqrt{13}}{13}$