Quadratic Equations Long Questions (Question 9 - 12)


Question 9:
Diagram above shows a rectangle ABCD.
(a) Express the area of ABCD in terms of m.
(b) Given the area of ABCD is 60 cm2, find the length of AB

Solution:
(a)
Area of ABCD
= (n + 7) × n
= (n2 + 7n) cm2

(b) 
Given the area of ABCD = 60
n2 + 7n = 60
n2 + 7n – 60 = 0
(n – 5) (n + 12) = 0
n = 5    or    n = – 12 (not accepted)

When n = 5,
Length of AB = 5 + 7 = 12 cm