Could someone please explain how to write an equation.

Question

Write an equation for the following transformation of y=x; a vertical stretch by a factor of 4.

I'm not sure but this is what I tryed
y=f(x)
vertical stretch 4
y=f(x+4)
y=4

Answer 1

no,
a vertical stretch of 4 for y = x would give us
y = 4x

e.g. suppose you have (2,2) on the first graph.
That point lies 2 units above the x-axis, you want to "stretch" that by a factor of 4, so it would be 8 units high
in y = 4x, when x = 2, y = 8

(your equation of y = f(x+4) would be a horizontal shift of 4 units to the left )