a) x-12/4 = 1/2
⇔x -12 = 1 x 4
⇔x - 12 = 4
⇔x = 16
b)(x . 6 2/7 + 3/7).2 1/5 - 3/7 = -2
⇔ (x . 44/7 + 3/7). 11/5 - 3/7 = -2
⇔ x . 44/7 + 3/7 . 11/5 - 3/7 = -2
⇔ x . 44/7 + 33/35 - 3/7 = -2
⇔ x . 44/7 = -2 + 3/7 - 33/35
⇔x . 44/7 = -88/35
⇔x = -2/5
c)(x + 1/5)² + 17/25 = 26/25
⇔(x + 1/5)² = 26/25 - 17/25
⇔(x + 1/5)² = 9/25
⇔(x + 1/5)² = (3/5)²
⇔x + 1/5 = 3/5
⇔x = 2/5