When the exchange rate is $1.5 to the £, the number
of dollars you would get for £x can be found from y
= 1.5x.The graph of this relationship is a straight line.
There is said to be a linear relation between the number of
pounds and the number of dollars.
generally, any relation of the form y = ax + b where a and b
are constants, is a linear relation. The graph is a straight
example, a spring of unstretched length 6cm is such that it
stretches by 0.5 cm for every 100 grams load suspended on
it. Its length y cm with a load of x hundreds of grams is
given by y = 0.5x + 6. The graph of this relation is a straight