原代码为
S1 = MathTex('S_1=\\sum_{k=0}^\\infty \\sum_{a=0}^\\infty (\\frac{3}{5})^k(\\frac{2}{5})^{a+k}a\\binom{a+k}{k}',font_size=36)
S2 = MathTex('S_2=\\sum_{k=0}^\\infty \\sum_{a=0}^\\infty (\\frac{3}{5})^k(\\frac{2}{5})^{a+k}k\\binom{a+k}{k}',font_size=36)
S3 = MathTex('S_3=\\sum_{k=0}^\\infty \\sum_{a=0}^\\infty (\\frac{3}{5})^k(\\frac{2}{5})^{a+k}\\binom{a+k}{k}',font_size=36)
jieshi3 = VGroup(
VGroup(
Text('这里，我们设',font_size=32),
S1
).arrange(RIGHT,buff=0.1),
S2,
S3
).arrange(DOWN,buff=0.1)
网页链接 (
FadeOut(E_2),
FadeOut(E_2_1),
FadeOut(E_2_2)
)
self.play(Write(jieshi3))
self.wait()
jieshi4 = VGroup(
Text('那么',font_size=32),
MathTex('E_2=\\frac{9}{25}(S_1+2S_2+2S_3)',font_size=36)
).arrange(RIGHT,buff=0.1)
self.play(ReplacementTransform(jieshi3,jieshi4))
self.wait()
self.play(Unwrite(jieshi4))
self.wait()
self.play(FadeIn(S3))