X/(x + 4) + x /(x - 4)= 50/9
( x² - 4x + x² + 4x) / ( x² - 16) = 50/9
2x² / ( x² - 16) = 50/9
50( x² - 16) = 9 × 2x²
50x² - 800 - 18x² = 0
32x² - 800 = 0
x² - 25 = 0
D = b² - 4ac = 0² - 4 × 1 × ( - 25) = 100 = 10²
x₁ = 10/2 = 5
x₂ = - 10/2 = - 5
(5x + 7) / ( x - 2) - ( 2x + 21)/(x + 2) = 26/3
( 5x² + 17x + 14 - ( 2x² + 17x - 42)) / ( x² - 4) = 26/3
( 5x² + 17x + 14 - 2x² - 17x + 42) / (x² - 4) = 26/3
( 3x² + 56)/ ( x² - 4) = 26/3
26( x² - 4) = 3( 3x² + 56)
26x² - 104 = 9x² + 168
26x² - 9x² - 168 - 104 =0
17x² - 272 = 0
x² - 16 = 0
D = b² - 4ac = 0² - 4 × 1 × ( - 16) = 64 = 8²
x₁ = 8 / 2 = 4
x₂ = - 8 / 2 = - 4