The following data represents the normal monthly precipitation for a certain city.( i will post the table)
draw a scatter diagram of the data for one period. find the sinusoidal function of the form (i will post) that fits the data.

Step-by-step explanation:

Use a sinusoidal function of the form

A is the amplitude, obtain the difference between the highest and the lowest value, and then divide by two:

D is the vertical shift, is equal to the lowest value plus the amplitude:

B is the frequency, being 12 months for each cycle (period T=12) and the relation between the period and the frequency is:

Finally, for C the phase shift, the highest value in a  sine function the highest point is in the first quartes of the period if the period is 12, then this maximum is in x=3. In the data the highest is in x=7, so the phase shift is to the right and equal in value to 4 (C=4).

So:

For the form

multiply C by B to find E ():

x = -3

y = -18

step-by-step explanation:

to solve by substitution, substitute one variable and solve for the other. then substitute again to find the remaining variable.

x-1/3(3x-9) = -3 since y=3x-9 substittute y.

x-1/3(3x-9)=-3

x + x +3 = -3

2x+3=-3

2x+3-3= -3-3

2x=-6

x=-3

substitute again into y=3x-9

y=3(-3)-9

y=-9-9

y=-18