JAMB Mathematics Past Questions & Answers - Page 22

106.

Given that r = \( \sqrt \frac{3v}{\pi h} \), make v the subject of the formula

A.

v = 3 \(πr^2\) h

B.

v = \(\frac{πrh}{3}\)

C.

v = \(\frac{πr^2h}{3}\)

D.

v = 3πrh

Correct answer is C

square both sides to remove the big square root

→ r\(^2\) = \(\frac{3v}{πh}\)

cross multiply

3v = r\(^2\) * πh

v = \(\frac{πr^2h}{3}\)

107.

If A = \(\begin{pmatrix} 2 & 1 \\ 2 & 3 \\ 1 & 2 \end{pmatrix}\) and B = \(\begin{pmatrix} 3 & 2 \\ 4 & 2 \end{pmatrix}\). Find AB

A.

\(\begin{pmatrix} 18 & 6 \\ 12 & 10 \\ 10 & 6 \end{pmatrix}\)

B.

\(\begin{pmatrix} 10 & 6 \\ 13 & 10 \\ 12 & 6 \end{pmatrix}\)

C.

\(\begin{pmatrix} 10 & 6 \\ 12 & 10 \\ 11 & 6 \end{pmatrix}\)

D.

\(\begin{pmatrix} 10 & 6 \\ 18 & 10 \\ 11 & 6 \end{pmatrix}\)

Correct answer is D

Given A = \(\begin{pmatrix} 2 & 1 \\ 2 & 3 \\ 1 & 2 \end{pmatrix}\) and B = \(\begin{pmatrix} 3 & 2 \\ 4 & 2 \end{pmatrix}\).

We can multiply these matrices since the number of colums in A = number of rows in B

 

AB = \(\begin{pmatrix} (2*3)+(1*4) & (2*2)+(1*2) \\ (2*3)+(3*4) & (2*2)+(3*2) \\ (1*3)+(2*4) & (1*2)+(2*2) \end{pmatrix}\)

 

AB = \(\begin{pmatrix} (6+4) & (4+2) \\ (6+12) & (4+6) \\ (3+8) & (2+4) \end{pmatrix}\)

 

= \(\begin{pmatrix} 10 & 6 \\ 18 & 10 \\ 11 & 6 \end{pmatrix}\)

 

108.

Integrate (2x+1)\(^3\)

A.

\(\frac{{2x+1}^3}{8}\) + C

B.

\(\frac{{2x+1}^4}{8}\) + C

C.

\(\frac{{2x+1}^4}{4}\) + C

D.

\(\frac{{2x+1}^2}{6}\) + C

Correct answer is B

Recall chain rule: 

u = 2x +1; du = 2dx → dx = \(\frac{du}{2}\)
u\(^3\) = ∫ u\(^3\) \(\frac{du}{2}\) → \(\frac{1}{2}\) ∫ u\(^3\)

=  \(\frac{1*u^4}{2*4}\) 

=  \(\frac{u^4}{8}\) →  \(\frac{{2x+1}^4}{8}\) + C

109.

In how many ways can the letter of ZOOLOGY be arranged?

A.

720

B.

360

C.

840

D.

120

Correct answer is C

Zoology has 7 letters in total, with O repeated thrice

\(\frac{7!}{3!}\) → \(\frac{7*6*5*4*3*2*1}{3*2*1}\)

= 840ways

110.

In the diagram above angle LNM and angle YNZ are represented by g and h respectively. Find ∠MNY

A.

180º - gº - hº

B.

360º - (g-h)º

C.

180º - (g-h)º

D.

360º - gº - hº

Correct answer is A

Using line LZ with angles sum = 180º

: ∠MNY = 180º - (g + h)º or 180º - gº - hº