1977-06-22 — Page 19

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育教僑華頁三第張五第日六初月五年巳丁屦夏

1977中學會考試題預習專欄

明德社主編

WAH KIU YAT PO

-1000[1-(0.98)}_m_

=1.000 - 1000(0.98)") m

(c) The total distance. the

train travelled until

it came to a stop

│數學 - ®

同等課程:

※和建議答案室

20 1-0.98

1000 m

女長波

Suggested Solations

"For HKCEE 1977

Mathematics 28

Section B

11. Soltuion(a) AOB 15°x2

=30°=

The length of the radius DA

inte

30

cm

b) Area of the shaded sector

AOB-

1

2

sq.cm

75

sq.cm

(c) Area of BOC=

sin

sq.cm

225

T

Sq.cm

Area of sector BOC=

m

14.Given ABCD is a cyclic

quad. AD//EC

To find (a) which two

triangle are similar to PAD (b)If PB-8cm,PC

10mm, Find BE

Solution:(a) Since EC//AD

(Given)

ECP PAD

corr. s EC//AD

ECP ADP

corr. s EC

EPC APD

Commom)

PAD PEC

are similar (Equiangu-

lar)

PBC=LPDA (Ext, ¿cyclic quad) ZBCP PAD (Ext./cyclic quad) ZBPC=/APD (proved)

PAD are similar (Equiangu-

lar)

PCB

APEC and PBC are the tri-

andles dimilar toSPADI

(b) Since PEC,PCB abd PAD

are similar to each other.

PB PC RC

=

PE (Equiangular

10.78 10

TO

PE =

7=3+k

1.e. k=-2

郭日僑華

(b) since 2x2+x-8=0

1.e. 2x-8-x=0 i.e.

i.e. x2-2-2- ~

The equation of the line added to the graph is

-y=2-

The solution of 2x+x=8=0· are x=-2.3 or 1.80

ー數學試卷建議答案全卷完

岑俊彦·

Suggested Solutions:

For HKCEE 1977:

Additional Mathematics. 9(a)

·P63,00

From the diag

w=

三期星

(a) y=x(x -7).

At A,D, y=0·

x=0,± √%

日二十月六年七七九一屦公年六十六國民中

For stationary points,

x = (x2 -7)3 +x•3(x −7)2 .(2x)

= (x2-7 )? ¦ ×2 −7+6x2 }

=7\x2 -7)2 (x2-1)=0

17 or+1

y=0 or+216

A(−17,0),B(-1,216),

C(1,-216),D(7,0)

(b)

Let I = f x(x-7) dx

If u=x-7

du-2xdx

1 (x^-7) xx

= = U+C

du

=}(x2-7} +C

Ans.

Ans

(c) Since the regions ABO and

OCD are the same, we have

Area of shaded regions

dx

=2 fyax=2 ["x(x2 -7.)3 d

(b) AX +Bxy+Cy ±4.

Since it passes through

p(1, 13) and Q(1, - £3)

A(1) +B(1)(-2)+C(-)-4

A+

√3B+20=4

and A(1)2+B(1) (~~~) +0(−−−2}

1.e. A-

and 3 give B=0

Now, AX + Cy=4

An's.

©

Differentiate with respect to x:

2Ax+20y

*

A(1)+c()=0 asp(12)

A-12 C=O and X

4A-C-0

also p(1,2) lies on

A(1) +C(3)2=4

A+ 2/2 C-4

4A+3C =16

Solving (5 and 6, we have

A-T

C=4

The curve Ax +cy.

TC-radius

=r

The equation of the circle.

-2. (x-7)" from resultof (b) 금 (-7)

i.e. x2+4y2=4

is an ellipse.

is (x−m)2+(y—n) =m2

Ans.

and t

sq.cm

Area of the segment BDC.

375

225

150

sq.cm

Solution

BE =

122

8cm

4 cm

15. Given:AS ABD, OBE are.

equilateral tri- angles

To prove:(a)ABES DBC

(b) A,B,C,D,K,

are conecyclic (c) Calculate

LAKC

Since it passes through P(2,0),

• (2-m) + (0-n)2 -m2

4-4m+m2+n2=m2

4m=n2+4

(b) m=

n=

Ans.

(a) DAF CBF 50°

Draw AG DF

DAG FAG-25°

DG=1xsin25°m=0:4226m

DP=2x014@ptim= 1

(b) BD= 2 +1. m

(c) Cin/DBG=

AN,

0.4226

2.236.

LDBG 10°54

LDBF=2x1.0° 54

21°48'

13.Solution(a) The distance that the train travelled

in the nth sec...

=20(0.98)

FIL

(b) The total distance that

the train travelled in

the first n seconds.

20(1-(0.98)")

1-0.98

m:

Proof:(a) Since AsABD, CBE

are equilaterala

(Given)

AB=BD; BE BC

LABD = LOBE 7·60°. (properties of eg.. ZABD+LABC= 2GBE+ ZABC 1.e.4ABE=4DBC

ABEDBC(S.A.s)

(b) ¿CDB=¿BAE (corr..s=15)

A,B,D,K,are concyclic (converses in the same.

segment)

:(0)| ÷ AKD=LABD (is in the same

segment)

Since ZABD=60° (proved)

AKD=60°

1.e.4AKC=180°-60° {Adj...... S

on st.line)

=120°

16.Solution:(A)Since P(3,7)

lies on the graph y=x +k

2401 sq.units.

11-4)y (2x2+3x+1)=1

Differentiate with respect

12. (A)

/ (b)

tox:

Ans

2m-2

Ans

2y¶x(2x3 +3x+1)+y^(6x+3=0

when?

x=0,y=1

t=2n

Ans.

Ans.

(c) Substituting m=

11

into 4n+4

have 4(2+2)=()+4

2(2+3)+4

16+85 t +16 t2 8s

the loucés of Q is given by

y =8x

Ans.

Differentiate again with respect to x:

20. (2x2+3x+1)+/

2yX(2x2 +3x+1)+

2y(6x+3)+2yx(6x+3)+

y2(12x)=0

Substituting dy ==, x=0,

y=1, we have

2 (−3 ) ( − } ) ( 1 ) + 2( 1 ) <¥(1)+

2(1) (~~) (3)+2 ( 1 ) (−) (3)+0=0

-9-9-0

dy

Lxx = 27

Ans.

t=coso+isino·

t =(cose+ising)

=cosno+isinnd- =cos(-n)+isin(-n

cosisin no

-n

=2cos no -2isin no

8cos 0=2(16cos 0)

=(2cosa)

= (t+t!).

= (t*+4t+6+4t+t^"")

An's

= 1⁄2 ((t"+t")+4(t+t3) +6

[2cos40+4.200320+6]

=cos40+4cos20+3 Comparing with

8cos" =cos40+AC0520+B

A=4

B3

(c) From (b),

8cos &=cos40+4cos28+3

Bcoso -2=c0s46+4cos20+1

put Bcost-2 =0, this becomes the given equation

cos40+4co520+1 =0

Now,

8cos Q-2=0

cos"Q

cose-1 or —

possible)

Q=45°,135°,225,or 315°.

Ans.

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