7. Find y when y"x² + (x² -81)y = -xy'.(10%)

4.Solve +y=x, y(0)=3.(10%)

(1) Find L{sin(2t)}. (5%) (Write down the detailed process)

(2) Solve +3y= 13sin(2t), y(0)=6.(15%)

6.Please write down the Bessel's differential equation. (7%)

8.Find the eigenfunction of the following equation: y"+ ky =0, y(0)-y(L)-0.(15%)

9. Find the Fourier series in complex form for the periodic function f(t) with period 2, .(18%) 

7. Bigly or Big League? "Did he say bigly?" This question had been asked repeatedly on social media soon after the then-candidate Donald Trump was reported to use the word during the first US presidential debate. Many wondered whether bigly was really an English word or a "Trumpism" presumably derived from big and the adverb suffix -ly. However, based on acoustic analyses, some phoneticians argued that what Mr. Trump actually said was big league but the final /g/ in his league was just difficult for the untrained ear to detect. Figure 2 shows the waveform and spectrogram of Trump's production of what appears to be Figure 1 Donald Trump, the to-be ambiguous between bigly and big league. Look at the figure. president of the most powerful What are the acoustic cues to final /g in league? Name at least  TWO of them.

Question 2-1. Use the substitution test described above to identify all constituents in the following sentence. Explain how you discovered the constituents. (20%) The tall man might have taken the pen away.

Question 2-2. Sometimes a test may give false negative results. That is, a word string is a constituent, but the results suggest otherwise. Therefore, syntacticians usually apply multiple diagnoses. In addition to substituting pronouns, we can use one. Consider this sentence: I met the guy with brown hair from the US, but not the one from the UK. Here one is substituted for guy with brown hair, indicating that guy with brown hair is a constituent. Apply this one substitution test to the sentence in the above question. Does this test reveal any more constituents than what you have just identified? Why or why not? (5%)

Question 3-1. Describe the trends and features in the graph. (10%)