# tangents

• Aug 26th 2008, 11:42 PM
psychosocial for life
tangents
i have two tangents that i have the equations to. the question asks to find the co-ordinates were the two tangents intersect. i am guessing that i will have use the two tangent equations in a similtaneous equation but i dont know how can some one help me ? the two equations are Y=5x-90 at x=5 and y=-16x-2024 at x=6
• Aug 26th 2008, 11:54 PM
11rdc11

$\displaystyle 5x - 90 = -16x -2024$

$\displaystyle 21x = -1934$

$\displaystyle x = \frac{-1934}{21}$

so now just plug in x into one of your original equations and it will give you your y

If you have any questions feel free to ask.
• Aug 27th 2008, 12:30 AM
psychosocial for life
im still having trouble with it im getting an y value of -550.47 this is far to great to be real on my graph i think the problem lies in thi equation y=-16x-2024
my dy/dx was 3x^2-12x-31 ax was 6 could some one see if they got the same answer as me
• Aug 27th 2008, 12:34 AM
11rdc11
What was the original function before you took the derivative and what was the original question you were working on?
• Aug 27th 2008, 12:54 AM
psychosocial for life
x^3-6x^2-31x+120 was the original function the question was to take a point one with a posotive gradient and one with a negative gradient on the cubic that i found from the equation x^3-6x^2-31x+120 and draw a tangent i then had to work out the tangent equation. i then had to extend the tangents until they intersect and find the co-ordinate at which they intersect