Solve the equation: ① x2-2x-8 = 0 (by formula method) & nbsp; & nbsp; ② 2x2-4x + 1 = 0 (matching method) ③ (x + 1) (x + 3) = 15 & nbsp; & nbsp; & nbsp; & nbsp; & nbsp; & nbsp; & nbsp; & nbsp; & nbsp; & nbsp; & nbsp; & nbsp; & nbsp; ④ (Y-3) 2 + 3 (Y-3) + 2 = 0

Solve the equation: ① x2-2x-8 = 0 (by formula method) & nbsp; & nbsp; ② 2x2-4x + 1 = 0 (matching method) ③ (x + 1) (x + 3) = 15 & nbsp; & nbsp; & nbsp; & nbsp; & nbsp; & nbsp; & nbsp; & nbsp; & nbsp; & nbsp; & nbsp; & nbsp; & nbsp; ④ (Y-3) 2 + 3 (Y-3) + 2 = 0

① ∵ x2-2x-8 = 0 a = 1, B = - 2, C = - 8, ∵ x = − B ± B2 − 4ac2a = 2 ± 362 = 1 ± 3, the solution is X1 = 4, X2 = - 2; ② from the original equation, we get x2-2x = - 12, the two sides of the equation plus the square of half of the coefficient of the first term, we get x2-2x + 1 = 12, formula, (x-1) 2 = 12, the solution is X1 = 1 + 22, X2 = 1-2