Calculating Curve Tangent at x=-π/4

[SwedishFred]

Homework Statement

Deside curve tangent in point x=-π/4

Homework Equations

f(x)=1/3sin(3x-π/4)
y=f(x)

The Attempt at a Solution

f`(-π/4)=-1
using the tangent equation
y=kx+m
y=-1*(-π/4)+m
y=1/3sin(3(-π/4)-π/4)
≈3.33*10^-14
3.33*10^-14=-1*(-π/4)+m
f(x)≈-1*(-π/4)+0,79
is this right ? I have a bad feeling...

 

[Mark44]

Homework Statement

Deside curve tangent in point x=-π/4

Deside?
What is that?
Is the problem to find the line that is tangent to the curve at x = -π/4?

Homework Equations

f(x)=1/3sin(3x-π/4)
y=f(x)

The Attempt at a Solution

f`(-π/4)=-1
using the tangent equation
y=kx+m
y=-1*(-π/4)+m
y=1/3sin(3(-π/4)-π/4)
≈3.33*10^-14

No.
When x = -π/4, y = 1/3 * sin(3(-π/4)-π/4)) = 1/3 * sin(-π). This is one of the angles whose sine and cosine you should have committed to memory. It looks like you might be using a calculator to do this, and either have the calculator in the wrong mode (it should be in radian mode) or you are using an approximation to π. Either way will not give you the right answer.

3.33*10^-14=-1*(-π/4)+m
f(x)≈-1*(-π/4)+0,79
is this right ? I have a bad feeling...

 

[Mark44]

By the way, questions that involve taking derivatives should be posted in the Calculus & Beyond section, not in the Precalculus section.