<u>Step-by-step explanation:</u>
Use the formula y = A cos (Bx - C) + D where
- A = amplitude
- Period = 2π/B
- Phase Shift = C/B
- D = vertical shift (aka midline)
Given: Max = 8, Min = 2, (1/2)Period = 20 → Period = 40
Amplitude (A) = (Max - Min)/2
= (8 - 2)/2
= 6/2
= 3
Midline (D) = (Max + Min)/2
= (8 + 2)/2
= 10/2
= 5
Period = 2π/B
→ B = 2π/Period
= 2π/40
= π/20
Notice that the Minimum touches the y-axis (not the Max) so there is no phase shift but there is a reflection → C-value = 0 & A-value is negative
Now, let's put it all together:
A = -3, B = π/20, C = 0, D = 5