Plz Help , stuck on final exercise !

Plz Help with the following math problem ! I really appreciate it ! :

Two pure notes of the same amplitude and of frequencies 15 Hz. and 17 Hz. sounded together to produce beats. Each note is modeled as a sine wave.

Quests :

a - What values should the constants a and b take in the function Y1 = sin(at) + sin(bt) if it is to model the sound of the two notes playing together ?

b - What values should the constants c and d take in the function Y2 = 2 sin(ct) cos(dt) if it is to model the sound of the two notes playing together ?

c - Plot both functions Y1 and Y2 on your calculator,choosing a suitable window to show the beats over a period of one second , and then sketch what is on the screen , labeling the axes.

Thanksss in advance !