How to transform only a part of formula?

[gargVader]

formula2=TexMobject(r"\frac { d }{ dx } f(x)\quad =\quad \underset { h\rightarrow 0 }{ lim } \frac { f(x+h)\quad -\quad f(x) }{ (x+h)\quad -\quad (x) } ")
formula2.set_color(BLUE)
self.play(Write(formula2), run_time=5)
self.wait(3)
#
formula3=TexMobject(r"\frac { d }{ dx } f(x)\quad =\quad \underset { h\rightarrow 0 }{ lim } \frac { f(x+h)\quad -\quad f(x) }{ h } ")
formula3.set_color(BLUE)
self.play(ReplacementTransform(formula2, formula3))
self.wait(5)

[zavden]

With arrays, but it usually causes problems if you use the radical symbol. And use \overinstead \frac if use arrays.

        f1=TexMobject(
            r"\frac{d}{dx}f(x)\quad =\quad\lim_{h\to 0}{f(x+h)\quad-\quad f(x) \over ",
            r"(x+h)\quad-\quad(x)",
            "}"
            )
        f2=TexMobject(
            r"\frac{d}{dx}f(x)\quad =\quad\lim_{h\to 0}{f(x+h)\quad-\quad f(x) \over ",
            "h",
            "}"
            )
        self.add(f1)
        self.play(ReplacementTransform(f1[1],f2[1]))
        self.wait()

[gargVader]

@zavden The code you gave is not working

[gargVader]

My earlier code: (Screenshot since the code feature on github is crappy)

`class test6(Scene):
def construct(self):
formula1=TexMobject("y\quad =\quad f(x)")
formula2=TexMobject(r"\frac { d }{ dx } f(x)\quad =\quad \underset { h\rightarrow 0 }{ lim } \frac { f(x+h)\quad -\quad f(x) }{ (x+h)\quad -\quad (x) } ")
formula3=TexMobject(r"\frac { d }{ dx } f(x)\quad =\quad \underset { h\rightarrow 0 }{ lim } \frac { f(x+h)\quad -\quad f(x) }{ h } ")

	formula1.set_color(RED)
	formula2.set_color(BLUE)
	formula3.set_color(BLUE)

	self.play(Write(formula1), run_time=3)
	self.play(ApplyMethod(formula1.shift, 3*LEFT + 3*UP))
	self.wait()
	#
	self.play(Write(formula2), run_time=5)
	self.wait(3)
	#
	self.play(Transform(formula2, formula3))
	self.wait(5)

`

[zavden]

What is the error?

class Help1(Scene):
    def construct(self):
        f1=TexMobject(
            r"\frac{d}{dx}f(x)\quad =\quad\lim_{h\to 0}{f(x+h)\quad-\quad f(x) \over ",
            r"(x+h)\quad-\quad(x)",
            "}"
            )
        f2=TexMobject(
            r"\frac{d}{dx}f(x)\quad =\quad\lim_{h\to 0}{f(x+h)\quad-\quad f(x) \over ",
            "h",
            "}"
            )
        self.add(f1)
        self.play(ReplacementTransform(f1[1],f2[1]))
        self.wait()

[gargVader]

done. thank you