Let line $l_1$ be the graph of $5x + 8y = -9$. Line $l_2$ is perpendicular to line $l_1$ and passes through the point $(10,10)$. If line $l_2$ is the graph of the equation $y=mx +b$, then find $m+b$.
+36916 5x+8y= -9 re-arrange in to y= mx + b form
8y = -5x - 9
y = -5/8 x - 9/8 shows m1 (the slope) = =5/8
Remember how to find pepindicular slope?
- 1 / m1 will be perpindicular -1 / (-5/8) = 8/5
so the line we are looking for is y = 8/5 x + b Now sub in the point given (10,10) to find the value of b
10 = 8/5 (10) + b b = -6
your line is y = 8/5 x - 6 m+ b = 8/5-6 = - 4 2/5
