X⁴ + x² - 1 = x⁴
x⁴- x⁴ + x² = 1
x² = 1
x = 1
x = - 1
√2x + 18 = x + 5
2x + 18 =( x + 5)²
2x + 18 = x² + 10x+ 25
- x² + 2x - 10x - 25 + 18 =0
- x² - 8x - 7 = 0
x² + 8x + 7 = 0
D = b² - 4ac = 64 - 4×7 =36 = 6²
x1 = ( - 8 + 6) / 2 = - 1
x2 = ( - 8 - 6) / 2 = - 7