Answer:
We first need to know the graph of the basic function belonging to the trigonometric family, which is sin x.
Now we need to apply basics of functions to get the graph of y = -sinx from y = sinx
If x is the input in the y = sinx , then sin x will be the output which will be represented on the y axis. Eg :
If x = pi/2
then output will be y = sin(pi/2) = 1
Hence in the graph of sinx, at x =pi/2 the value of y is 1.
Once we have understood this, we can use the same logic in the case
y = -sinx
If x = pi/2
then output will be y = - sin(pi/2) = -1
Here we can see that the output of y = - sin x will be the exact negative of of the output of y = sinx
Hence all portions of the graph of y = sinx in the +y axis will come down to the -y axis for y = -sin x, i.e we will be taking mirror image of the graph along the x axis. Below are the graphs of y=sinx and y= - sinx respectively for your reference:
(image courtesy Microsoft graphic calculator)