Consider two functions of time t:
f(t) = 0.01t^2
g(t) = 4t
where 0 < t < infinity.
Now consider the following two statements:
i. For some t > 0, g(t) > f(t).
ii. There exists a T such that f(t) > g(t) for all t > T.
Which one of the following options is TRUE?
A. only (i) is correct
B. only (ii) is correct
C. both (i) and (ii) are correct
D. neither (i) nor (ii) is correct
GATE 2023 · General Aptitude · Functions · medium
Answer: Both statements are correct; answer is C
Find the intersection(s) of f(t) and g(t): 0.01t^2 - 4t = 0 => t(0.01t - 4) = 0 => t = 0 or t = 400
Test statement (i): Does g(t) > f(t) for some t > 0?: Pick t = 1: g(1) = 4, f(1) = 0.01. Since 4 > 0.01, we have g(t) > f(t). Statement (i) is TRUE.
Test statement (ii): Does there exist T with f(t) > g(t) for all t > T?: Take T = 400. For t > 400: f(t) - g(t) = 0.01t^2 - 4t = t(0.01t - 4) > 0 since t > 0 and 0.01t > 4. Statement (ii) is TRUE.
Conclusion: Both (i) and (ii) are correct. Answer is C.