Posted by Lynnette on Thursday, September 23, 2010 at 6:08pm.
Find the line of the equation that
hits y=4x^220 when x= 5 that is
perpendicular to 5x6=3y
My solution does not graphical show perpendicular lines, but algebraically it works lol Help!

PreCalc  Reiny, Thursday, September 23, 2010 at 6:17pm
when x=5
y = 4(5)^2  20 = 80
so you have the point (5,80)
the slope of 5x6 = 3y is 5/3
so the slope of the required line is 3/5
Now use whichever method you normally use to find the equation of a line given its slope and a point on it.

PreCalc  Lynnette, Thursday, September 23, 2010 at 6:20pm
Hi Reiny, Yes, I got that far. I even came up with a line, but am looking to see what others get as my line, when graphed, is not perpendicular to the other line mentioned in the prob (5x6=3y)

PreCalc  Reiny, Thursday, September 23, 2010 at 6:29pm
since the new line has slope 3/5, its equation must be
3x + 5y = k
point(5,80) on it ....
15 + 400 = k = 385
so new equation is 3x + 5y = 385 or
y = (3/5)x + 77
Since the slopes are negative reciprocals of each other, their graphs MUST be perpendicular.
Check your calculation of points and check the plotting of points

PreCalc  Lynnette, Thursday, September 23, 2010 at 6:37pm
I hope you're right since that's the equation I got too! I may be entering things into my calculator wrong. Using that is new to me. Thanks for all you're help!
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