Question

Draw a graph of the equation 3x - y = 7. From the graph find the value of:
(i) y, when x = 1
(ii) x, when y = 8

Answer 1

We have 
3x - y = 7
⇒ -y = 7 - 3x
⇒ y = 3x - 7
When  x = -2
⇒ y = -6 - 7
= -13
When  x = 0
⇒ y = -7
When  x = 2
⇒ y = 6 - 7
= -1

x	-2	-1	0	1	2
y	-13	-10	-7	-7	-1

Thus ordered pairs of 3x - y = 7 are {(-2, -13), (-1, -10), (0, -7), (1, -4), (2, -1)}. Hence graph is as below.
(i) y, when x = 1
From graph we find that y = -4, when x = 1
(ii) x, when y = 8
From graph we find that x = 5, when y = 8.