Question

Help please! :)
Show that the line x+y+2 = 0 is a tangent to y = x^3 −4x, and find the point of contact.
[Hint: Find the equations of the tangents parallel to x+y +2 = 0, and show that one of
them is this very line.]

Answer 1

do you know how to find slope of tangent to y=x^3-4x ?

Answer 2

derive it 3x^2 - 4

Answer 3

yeah, so the tangent parallel to x+y+2= 0 will have the SAME slope as that of x+y+2=0
so whats the slope of x+y+2=0 ??

Answer 4

slope of that is -1?

Answer 5

can u find ?

Answer 6

so
-1 = 3x^2 - 4?

Answer 7

ok thank you i think i can do it now

Answer 8

oh great! welcome ^_^