Let’s Get Functional – SAT Math Question of the Day

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Let’s Get Functional – SAT Math Question of the Day

SAT Math Question of the Day
Explanation
In this question, we need to do operations between functions. Three functions p, q and r are described depending on the variable t. Function r is defined in terms of functions p and q as follows:

r(t) = p(t) − q(t)

We can plug the values of p(t) and q(t) into the equation above:

p(t) = t4
q(t) = 2t2
r(t) = t4 − 2t2

For t > 0, we are asked how r changes with increasing t (t gets farther from 0 means it increases in value). The increase ratio of t4 is higher than t2. This means that the value of r increases. However, there is a point we need to be careful about. At the beginning, the function characteristic may be different due to t4 − 2t2. For small values, 2t2 may be greater than t4. It is better to examine the function by assigning numbers for t:
t = 0
r(0) = (0)4 − 2(0)2 = 0
t = 1
r(1) = (1)4 − 2(1)2 = −1
t = 2
r(2) = (2)4 − 2(2)2 = 8
t = 3
r(3) = (3)4 − 2(3)2 = 63

We see that in the interval 0 < t < 1, r(t) first decreases from 0 to -1, and then increases from -1 to 8 and continues increasing as t gets farther from 0.

The correct answer is (D).

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