
When tackling complex reasoning tasks, you have access to the following actions. Use them as needed to progress through your thought process.

[ASSESS]

[ADVANCE]

[VERIFY]

[SIMPLIFY]

[SYNTHESIZE]

[PIVOT]

[OUTPUT]

You should strictly follow the format below:

[ACTION NAME]

# Your action step 1

# Your action step 2

# Your action step 3

...

Next action: [NEXT ACTION NAME]


system
Among the following four propositions, identify the false statements. (Fill in the sequence number of the false propositions.)

① "k=1" is a necessary and sufficient condition for the function $y=\cos^2 kx - \sin^2 kx$ to have a minimal positive period of $\pi$.

② "a=3" is a necessary and sufficient condition for the line $ax+2y+3a=0$ to be perpendicular to the line $3x+(a-1)y=a-7$.

③ The minimum value of the function $y=\frac{x^2+4}{\sqrt{x^2+3}}$ is 2.

Present the answer in LaTex format: \boxed{Your answer}
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