2018 MEXT Gakubu Maths B

QUESTIONS AND SOLUTIONS

 

I.   PART 1

 

QUESTION 01

If \(x > 0, y > 0\), and \(x + 3y = 2\), then \(\dfrac {1}{xy} \geq \bbox[10px, border: 2px solid red]{(1)}\) with equality if and only if \(x = \bbox[10px, border: 2px solid red]{(2)}\) and \(y = \bbox[10px, border: 2px solid red]{(3)}\).

 


QUESTION 02

The real-number solution to the equation \(2^{x + 2} - 2^{-x} + 3 = 0\) is \(x = \bbox[10px, border: 2px solid red]{(1)}\).

 


QUESTION 03

Let \(a, b\) be constants. If the polynomial \(x^4 + ax^3 + ax^2 + bx - 6\) is divisible by \((x - 1)^2\), then \(a = \bbox[10px, border: 2px solid red]{(1)}, b = \bbox[10px, border: 2px solid red]{(2)}\)

 


QUESTION 04

The maximum value of the function \(\sin 3x\) for \(\dfrac {5}{18} \pi \leq x \leq \dfrac 23 \pi \) is \(\bbox[10px, border: 2px solid red]{(1)}\), and the minimum value of that is \(\bbox[10px, border: 2px solid red]{(2)}\).

 


QUESTION 05

For the complex number \(z = \cos \dfrac 13 \pi + \sqrt{-1} \sin \dfrac 13 \pi\), the following equality holds: \(z + z^2 + z^3 + z^4 + z^5 = \bbox[10px, border: 2px solid red]{(1)}\).

 


QUESTION 06

Let S be a square with side length 1, T a triangle with side lengths \(1, 1, \sqrt{2}\) and R a triangle with side lengths \(1, \sqrt{2}, \sqrt{3}\). Let C be a pyramid with a base that is S and lateral faces consisting of two T's and two R's. The volume of C then is \(\bbox[10px, border: 2px solid red]{(1)}\).

 


II.   PART 2

 

On the xy-plane, a circle with center \((a, b)\) and radius \(r\) is tangent to the parabola \(y = x^2\) at two distinct points. Fill in the blanks with the answers to the following questions.

 

QUESTION 01

When one of the two points of tangency is \((t,t^2)\), express \(a, b\), and \(r\) in terms of \(t\).

\(a = \bbox[10px, border: 2px solid red]{(1)}\)

\(b = \bbox[10px, border: 2px solid red]{(2)}\)

\(r = \bbox[10px, border: 2px solid red]{(3)}\)

 


QUESTION 02

When one of the two points of tangency is \(\left( \dfrac 12, \dfrac 14 \right)\), express the area S of the finite region bounded by the circle and the parabola in terms of \(\pi\).

\(S = \bbox[10px, border: 2px solid red]{(1)}\)

 


III.   PART 3

 

Let \(f(x) = \int_0^x \dfrac {1}{1 + t^2} \: dt \quad x > 0\) and \(g(x) = f \left( \dfrac 1x \right)\).

 

QUESTION 01

Compute the derivatives \(f'(x) = \dfrac {d}{dx} f(x)\) and \(g'(x) = \dfrac {d}{dx} g(x)\).

\(f'(x) = \bbox[10px, border: 2px solid red]{(1)}\)

\(g'(x) = \bbox[10px, border: 2px solid red]{(2)}\)

 

QUESTION 02

Compute the value of \(f(1)\).

\(f(1) = \bbox[10px, border: 2px solid red]{(1)}\)

 

QUESTION 03

The function \(f(x) + g(x)\) is a constant \(C\). Find the value of \(C\).

\(C = \bbox[10px, border: 2px solid red]{(1)}\)

 

QUESTION 04

Calculate the limit \(\displaystyle \lim_{x \rightarrow \sim} \:f(x)\)

\(\displaystyle \lim_{x \rightarrow \sim} \:f(x) = \bbox[10px, border: 2px solid red]{(1)}\)

 


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