The graph of the line with equation ax by 1 is shown above

The graph of the line with equation ax + by = 1 is shown above. Which of the following must be true? a > 0 and b 0 and b > 0 a

Solution

ax +by =1

Re-arranging : by = 1 -ax

y = (-a/b)x + 1/b

From the graph we can see that slope of line <0 and y intercept is >0

So,y intercept is >0 ; 1/b>0 ---> b >0

Slope : a/b >0 ----> a >0

Option B