The polynomial function $\mathrm { I } ( \mathrm { t } ) = - 0.1 \mathrm { t } ^ { 2 } + 1.4 \mathrm { t }$ represents the yearly income (or loss) from a real estate investment, where t is time in years. After how many years does income begin to decline?
A) 6 yr
B) 14 yr
C) 7 yr
D) 9.33 yr

Question

Quizplus · Accepted Answer

The income begins to decline when the derivative of the income function, $I'(t) = -0.2t + 1.4$, equals zero. Solving $0 = -0.2t + 1.4$ for $t$ gives $t = 7$ years.

The Polynomial Function I(t)=−0.1t2+1.4t\mathrm { I } ( \mathrm { t } ) = - 0.1 \mathrm { t } ^ { 2 } + 1.4 \mathrm { t }I(t)=−0.1t2+1.4t

The Polynomial Function $\mathrm { I } ( \mathrm { t } ) = - 0.1 \mathrm { t } ^ { 2 } + 1.4 \mathrm { t }$