Text Solve: x4−13x2+36=0.x^{4}-13x^{2}+36=0.x4−13x2+36=0. Solution Let t=x2t=x^{2}t=x2 (with t≥0t\ge 0t≥0): t2−13t+36=0 ⇒ t=13±169−1442=13±52=9 or 4.t^{2}-13t+36=0\;\Rightarrow\; t=\frac{13\pm\sqrt{169-144}}{2}=\frac{13\pm 5}{2}=9\ \text{or}\ 4.t2−13t+36=0⇒t=213±169−144=213±5=9 or 4. From x2=9x^{2}=9x2=9: x=±3x=\pm 3x=±3; from x2=4x^{2}=4x2=4: x=±2x=\pm 2x=±2. x=±3, ±2 \boxed{\,x=\pm 3,\ \pm 2\,}x=±3, ±2