【用戶】Jiunndar Yeh
【年級】幼兒園下
【評論內容】(x + 1)(x + 2)(x + 3)(x + 4) - 120= [(x + 1)(x + 4)] * [(x + 2)(x + 3)] - 120= (x2 + 5x + 4)(x2 + 5x + 6) - 120= (x2 + 5x)2 + (4 + 6) * (x2 + 5x) + 4 * 6 - 120= (x2 + 5x)2 + 10(x2 + 5x) - 96 ... (-6) * 16 = -96, (-6) + 16 = 10= (x2 + 5x - 6)(x2 + 5x + 16) = (x + 6)(x - 1)(x2 + 5x + 16) = 0因當x2 + 5x + 16 = 0，此時其判別式b2 - 4ac = 52 - 4 * 16 = 25 - 64 = -39 < 0 故x2 + 5x + 16 = 0無實數解故得此方程式具x = -6, 1共兩實數解 ...選項(B)正確