Explanation for Question 21 From the Math (Calc) Section on the Official Sat Practice Test 9
Question 21 asks us the graph of the exponential function H and the X, 2 Y plane, or Y is equal to H of X has a Y intercept 3 of D or D is positive constant, 4 which of the following could define the function. H so there's a few key 5 things. And we know here, we know that it is an exponential function, 6 that it has a white interceptive D and that D is a positive 7 constant. Now thinking about the general form of an exponential 8 function, that's going to be, Y is equal to a B to 9 the power of X. So this to the power of X is the key 10 sign that we're working with an exponential function. 11 And from that alone, or going to get rid of both C and B, 12 because they don't have that to the power of X. 13 We're also given that the Y intercept is D and a 14 is the Y intercept. So let's substitute for variable of a, 15 for the variable D we had me beat the X. 16 What we're going to do now is we want to look at the two 17 choices that we're given and figure out in which scenario are we going 18 to be left with a positive Y intercept? 19 The Y intercept is when it crosses the Y axis. 20 So it's one X is equal to zero. So when X is equal to 21 zero, we want Y to be a positive number. 22 So let's plug in X is equal to zero. 23 For both of these expressions, we have H of X is equal 24 to negative three times D of 25 X. And here we know that X 26 is zero. So due to the zero is one. 27 So we have negative three times. One is equal to negative three. 28 So from that, we can get rid of a,...