oob73zj92b的部落格

標題:

HKDSE MATHEMATICS

發問:

1. The perimeter of a rectangle is 66cm. If its length by 3cm and its widthis decreased by 3cm, it’s new area is 14/15 times its original area. Find thedimensions of the rectangle.

最佳解答:

• maths_1111119@1@
• 我想問下有冇11月20日同21日既完全娛樂呀-
• 我22歲考完牌 我想問買IS200 保險有邊間保 最好平小小@1@

• maths_1111119@1@
• 我想問下有冇11月20日同21日既完全娛樂呀-
• 我22歲考完牌 我想問買IS200 保險有邊間保 最好平小小@1@

 

此文章來自奇摩知識+如有不便請留言告知

Inthe question, "If its length by 3 cm ......" should be "If itslength is increased by 3 cm". Let y cm be the length of the rectangle. Then, the width of the rectangle = (66 - 2a)/2 cm = (33 - a) cm (New area) = (14/15) x (Original area) (y + 3)[(33 - y) - 3] = (14/15)y(33 - y) 15(y + 3)(30 - y) = 14y(33 - y) 15(y + 3)(y - 30) = 14y(y - 33) 15y2 - 405y - 1350 = 14y2 - 462y y2 + 57y - 1350 = 0 (y - 18)(y + 75) = 0 y = 18 or y = -75 (rejected for length must be positive) 33 - y = 15 The dimensions of the rectangle: 18cm x 15 cm

其他解答: