During which stage of engine operation does the burning mixture of air and fuel force the piston downward?
a. compression
b. power
c. tdc
d. ignition

(b) Power.

Step-by-step explanation: Engine operation takes place in a number of stages, such as Intake, compression, combustion and Exhaust. In the stage of combustion (also known as Power), the hot burning mixture of fuel and air is ignited by heat generated due to high compression and so forcefully return the piston downwards.

Thus, the correct option is (b) Power.

(a) {a₁, a₁r, a₁r², … a₁rⁿ⁻¹, …}

(b) $59 398

step-by-step explanation:

(a) the annual sequence of profits

aₙ = a₁rⁿ⁻¹

the model for the sequence of profits is {a₁, a₁r, a₁r², … a₁rⁿ⁻¹, …} .

(b) profit after 15 yr

  a₁ = $ 30 000

  r = 1.05

a₁₅ = 30 000 × 1.05¹⁴

a₁₅ = 30 000 × 1.979 93

a₁₅ = $59 398

the profit in year 15 will be $59 398.