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MAT1320X Solution to Final Examination Summer 2020
Solution to the Final Examination
MAT1320X, Summer 2020
Part I. Multiple-Choice Questions
3 10 = 30 points
In all questions, (A) is the right answer.
1.1. The domain of the function f (x) = 1 ln( x e) is
(A) e < x 2e; (B) e x 2e; (C) x > 2e; (D) x < e.
Solution. 1 ln(x e) 0, ln(x e) 1, 0 < x e e, e < x 2e.
1.2. The domain of the function f (x) = 1 ln(e x ) is
(A) 0 x < e; (B) 0 x e; (C) x < 0; (D) x e.
Solution. 1 ln(e x) 0, ln(e x) 1, 0 < e x e, 0 x < e.
1.3. The domain of the function f (x) = 1 ln(e x ) is
(A) e < x 0; (B) e x < 0; (C) x < e; (D) x 0.
Solution. 1 ln(e + x) 0, ln(e + x) 1, 0 < e + x e. e < x 0.
2.1. Some values of functions f (x) and g(x), and their derivatives f '(x) and g'(x) are given in the
following table:
x f (x) f '(x) g(x) g'(x)
1 3 1 2 3
2 1 2 3 5
3 2 4 1 7
Let z = h(x) = (f g)(x), what is h(1) + h'(1)?
(A) 7; (B) 14; (C) 8; (D) 22.
Solution. h(1) = f (g(1)) = f (2) = 1. h'(1) = f '(g(1))g'(1) = f '(2)g'(1) = 2 3 = 6. h(1) + h'(1) = 7.
2.2. Some values of functions f (x) and g(x), and their derivatives f '(x) and g'(x) are given in the
following table:
1
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MAT1320X Solution to Final Examination Summer 2020
x f (x) f '(x) g(x) g'(x)
1 1 1 3 3
2 3 2 1 5
3 2 4 2 7
Let z = h(x) = (f g)(x), what is h(1) + h'(1)?
(A) 14; (B) 7; (C) 8; (D) 20.
Solution. h(1) = f (g(1)) = f (3) = 2. h'(1) = f '(g(1))g'(1) = f '(3)g'(1) = 4 3 = 12. h(1) + h'(1) =
14.
2.3. Some values of functions f (x) and g(x), and their derivatives f '(x) and g'(x) are given in the
following table:
x f (x) f '(x) g(x) g'(x)
1 3 1 1 3
2 1 2 3 5
3 2 4 2 7
Let z = h(x) = (f g)(x), what is h(2) + h'(2)?
(A) 22; (B) 14; (C) 7; (D) 8.
Solution. h(2) = f (g(2)) = f (3) = 2. h'(2) = f '(g(2))g'(2) = f '(3)g'(2) = 4 5 = 20. h(2) + h'(2) =
22.
2
e( x )
3.1. The derivative of the function f (x) = at x = 2is
x
7 4 4 4 7 4 3 4
(A) e ; (B) e ; (C) e ; (D) e .
4 3 3 4
2 2 2
2 x 2e x e x e x (2 x 2 1) 7
Solution. By the quotient rule, f '(x) = 2
2
. When x =2, f '(2) = e4 .
x x 4
sin 2 x
3.2. The derivative of the function f (x) = at x = is
x 4
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MAT1320X Solution to Final Examination Summer 2020
2 x sin x cos x sin 2 x
Solution. (B) By the quotient rule, f '(x) = 2
. When x = ,
x 4
1 1
2 2 2 4( 2)
f ' .
4
2
2
4
(ln x ) 2
3.3. The derivative of the function f (x) = at x = e is
x
(A) e2; (B) e; (C) e−1; (D) e2.
ln x
2 x (ln x ) 2
x ln x (2 ln x )
Solution. (E) Use the quotient rule. f '(x) = 2
. When x = e, f '(e)
x x2
= e−2.
(11 3x ) e x 1
2
4.1. Let f (x) = . Then f '(1) =
( x 1) 3 2 x
9 5 7 5
(A) ; (B) ; (C) ; (D) .
2 2 3 4
Solution. Taking the logarithm on both sides,
2 1
ln f (x) = ln(11 3x ) ( x 2 1) ln( x 1) ln(3 2 x) .
3 2
Then take the derivative with respect to x on both sides:
f '( x ) 2 1 1
2x .
f ( x) 11 3x x 1 3 2x
2 1 1
f '(x) = f (x) 2x .
11 3x x 1 3 2x
(11 3) e0 2 1 9
When x = 1, f (1) = 2 , f '(1) = 2 2 1 .
2 1 8 2 2
(3x 11)1/ 3 e x 1
2
4.2. Let f (x) = . Then f '(1) =
( x 3) x 5
3
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MAT1320X Solution to Final Examination Summer 2020
5 7 5 9
(A) ; (B) ; (C) ; (D) .
4 3 2 2
Solution. Taking the logarithm on both sides,
1 1
ln f (x) = ln(3x 11) ( x 2 1) ln( x 3) ln( x 5) .
3 2
Then take the derivative with respect to x on both sides:
f '( x ) 1 1 1
2x .
f ( x ) 3x 11 x 3 2( x 5)
1 1 1
f '(x) = f (x) 2x .
3x 11 x 3 2( x 5)
( 3 11)1/ 3 e0 1 11 1 1 5
When x = 1, f (1) = , f '(1) = 2 .
22 2 28 2 8 4
(2 x 5) e x 4
2
4.3. Let f (x) = . Then f '(2) =
( x 4) 3x 7
7 9 5 5
(A) ; (B) ; (C) ; (D) .
3 2 2 4
Solution. Taking the logarithm on both sides,
2 1
ln f (x) = ln(2 x 5) ( x 2 4) ln( x 4) ln(3x 7) .
3 2
Then take the derivative with respect to x on both sides:
f '( x ) 4 1 3
2x .
f ( x ) 3(2 x 5) x 4 2(3x 7)
4 1 3
f '(x) = f (x) 2x .
3(2 x 5) x 4 2(3x 7)
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