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Year 10 Interactive Maths - Second Edition


Problem Solving

We can use the Distributive Law and/or perfect squares to express the area of figures in terms of a variable, x.

Example 12

The length of the side of a square paddock is x m.  If one side of the paddock is lengthened by 8 m and the adjacent side is shortened by 3 m so as to make the paddock rectangular, find:  (a)  an expression for the area, A, of the rectangular paddock in terms of x,  (b)  the value of x, when the area of the rectangular paddock is 80 m squared, (c)  the area of the square paddock

Solution:
(a)  l = (x + 8) m, w = (x - 3) m.

Thus A = lw = x squared + 5x - 24.

a square of side-length x m and a rectangle of length (x + 8) m and width (x - 3) m
(b)  If A = 80, then x = 8.

(c)  Area of the square paddock = 64 m squared.

 

Example 13

A square picture is fixed in the middle of a square picture frame as shown in the diagram.  If the width of the border is x cm, express:  (a)  the length, l cm, of the frame in terms of x   (b)  the area, A cm squared, of the frame in terms of x.

Solution:

(a)  l = 17 + 2x

(b)  A = 289 + 68x + 4(x squared)

 

 

The square picture and square picture frame.


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