I need to graph $y=-2\cos3x$
I just went the standard route and reflected across the x axis, multiplied the y axis by 2 and multiplied the x axis by three. Is this incorrect? I got the wrong answer but I am not sure why.
I need to graph $y=-2\cos3x$
I just went the standard route and reflected across the x axis, multiplied the y axis by 2 and multiplied the x axis by three. Is this incorrect? I got the wrong answer but I am not sure why.
What you said sounds correct, though Theo makes a good point that "multiplying the $x$-axis by 3" might be where your problem is. This is what you should be seeing at each step:
Consider what happens when you solve the equation for $x$. You get $x=\frac{1}{3}\ldots$, not $x=3\ldots$. Thus, whatever you mean by "multiplying an axis by a factor", your two multiplications can't both be right, since what corresponds to the factor $2$ for $y$ is a factor of $\frac{1}{3}$ for $x$, not $3$. (Alternatively, you can divide by $2$ to see that what corresponds to the factor of $3$ for $x$ is a factor of $\frac{1}{2}$ for $y$, not $2$.)