URGENT F2 MATHS!!!

[匿名]

2012-06-15 2:35 am

1. If the sum of interior angles of a polygon is greater than triple of the sum of its exterior angle by 900degree, find the number of sides of the polygon

2. Three years ago, A's age is twice that of B. A's present age is 18 years less than 3 times the present age of B. Let the present age of A and B be x and y respectively, find the present ages of A and B.

回答 (1)

用戶2053

2012-06-15 2:59 am

✔ 最佳答案

1)Let n be the number of sides of the polygon :Sum of interior angles of the polygon = (n - 2)180°
Triple of the sum of its exterior angle = 3 * 360° ∴ (n - 2)180° = 3 * 360° + 900°
180n - 360 = 1980
180n = 2340
n = 13The number of sides of the polygon is 13.

2)Three years ago, A's age is twice that of B :
x - 3 = 2(y - 3) ...... (1)A's present age is 18 years less than 3 times the present age of B :
x = 3y - 18 ...... (2)Substitute (2) into (1) :3y - 18 - 3 = 2(y - 3)
3y - 21 = 2y - 6
y = 15By (2) :
x = 3(15) - 18 = 27The present ages of A is 27 and B is 15.

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