MATHEMATICS PAPER 1 GRADE 12 NSC EXAMS PAST PAPERS AND MEMOS NOVEMBER 2018
MEMORANDUM NOTE:
If a candidate answers a question TWICE, only mark the FIRST attempt. Consistent Accuracy applies in all aspects of the marking memorandum. QUESTION 1
1.1.1
x2 − 4x + 3 = 0 (x −3)(x −1) = 0 x = 3 or x =1
✔factors/correct subt in formula ✔x = 3 ✔x =1 (3)
1.1.2
✔substitution into the correct formula ✔x = 0,72 ✔x = 0,28 (3)
1.1.3
x2 − 3x − 10 > 0 (x − 5)(x + 2) > 0
OR x < −2 or x > 5
✔factors/ critical values ✔✔x < −2 or x > 5 (3)
1.1.4
3√x = x − 4 9x = x2 − 8x + 16 x2 − 17x + 16 = 0 (x −16)(x −1) = 0 x =16 or x =1 NA
✔ squaring both sides ✔ ✔ factors ✔ answer with selection (4)
OR
OR ✔ standard form ✔ recognize ✔ factors ✔ answer with selection (4)
1.2
2y + 9x2 = -1......(1) 3x − y = 2 ...... (2) y = 3x − 2 .......(3) 2(3x - 2) + 9x2 = -1 6x - 4 + 9x2 = -1 9x2 + 6x - 3 = 0 3x2 + 2x - 1 = 0 (3x - 1)(x + 1) = 0 x = 1 /3 or x = -1 y = −1 or y = −5
OR
2y + 9x2 = -1 ....... (1) 3x - y = 2 .........(2) x = y + 2 3 2y + 9 (y + 2 )2 = -1 ( 3 ) 2y + 9 (y2 + 4y + 4) = -1 9 2y + y2 + 4y + 4 + 1 = 0 y2 + 6y + 5 = 0 (y 5)(y + 1) = 0 y = -1 or y = -5 x = 1 /3 or x = -1
✔y = 3x − 2 ✔substitution ✔ standard form ✔factors ✔both x values ✔both y values (6)
OR
✔x = y + 2 3 ✔substitution ✔ standard form ✔factors ✔both y values ✔both x values (6)
1.3
✔33x = 4 ✔ ✔33x - 3 or 33x .3-1 ✔answer (4)
OR
✔33x - 3 or 33x .3-1 ✔33x = 4 ✔ ✔answer (4)
[23]
QUESTION 2
2.1.1
42
✔answer (1)
2.1.2
2a = 6 3a + b = 1 a + b + c = 2 a = 3 3(3) + b = 1 (3) + (–8) + c = 2 b = –8 c = 7 Tn = 3n2 + 8n + 7
OR
2a = 6 a = 3 Tn = 3n2 + bn + c T1 : 3 + b + c = 2 b + c = -1 ....(1) T2 : 12 + 2b + c = 3 2b + c = -9 ....(2) T2 - T1 : b = -8
Subst. in (1): – 8 + c = – 1 c = 7 Tn = 3n2 + 8n + 7
✔ a = 3 ✔ b = –8 ✔ c = 7 ✔Tn = an2 + bn + c (4)
OR
✔ a = 3 ✔ b = –8 ✔ c = 7 ✔Tn = an2 + bn + c (4)
2.1.3
T20 = 3(20)2 - 8(20) + 7 = 1047
✔substitution ✔answer (2)
2.2
Tn = −7n + 42 − 7n + 42 = −140 − 7n = −182 n = 26
✔Tn = −7n + 42 ✔− 7n + 42 = −140 ✔n = 26 (3)
2.3
✔ ✔simplification of Sn ✔equating ✔standard form ✔factors ✔answer with selection (6)
[16]
QUESTION 3
3.1
r = ½ and = S∞ = 6 S∞ = a 1 - r 6 = a 1 - ½ a = 3
✔substitution ✔answer (2)
3.2
Tn = arn-1 T8 = 3(1 /2 )7 T8 = 3 128
✔✔ T8 = 3(1 /2 )7 (2)
3.3
✔ r = 1 /2 ✔substitution ✔simplification ✔answer (4)
3.4 ✔expansion ✔ expansion ✔ answer (3)
OR
✔4p (3) OR
✔4p (3)
OR
✔ substitution and answer ✔substitution and answer ✔4p (3)
[11]
QUESTION 4
4.1
Yes For every x-value there is only one corresponding y value OR One to one mapping (vertical line test)
✔answer ✔reason (2)
4.2
R(–12 ; –6)
✔answer (1)
4.3
f (x) = ax2 substitute (-6 ; -12) −12 = a(−6)2 a = −1 /3
✔substitution ✔answer (2)
4.4
f : y = −(1 /3 ) x2 f-1 : x = −(1 /3 ) y2 y2 = -3x y = ± √− 3x Only y = −√-3x and x ≤ 0
✔swapping x and y ✔y2 = -3x ✔y = − √-3x (3)
[8]
QUESTION 5
5.1
Domain: x∈R ; x ≠1
OR
x∈(−∞;1)∪(1;∞)
✔answer (1)
5.2
x = 1 y = 0
✔x = 1 ✔y = 0 (2)
5.3
✔ y intercept ✔vertical asymptote ✔shape (3)
5.4
x ≥ 0 ; x ≠1
OR
0 ≤x < 1 or x > 1
OR
x∈[0;1) ∪(1;∞)
✔x ≥0 ✔x ≠1 (2)
OR
✔ 0 ≤ x < 1 ✔ x > 1
[8]
QUESTION 6
6.1
y = mx + c m = 5 + 1 4 - 0 m = 1 c = 1 g(x) = x + 1
OR
y = mx + c 5 = m(4) +1 m = 1 g(x) = x +1
✔substitution into gradient formula ✔y-intercept (0 ; 1) (2)
OR
✔substitute (4 ; 5) ✔c = 1 (2)
6.2
x2 − 2x − 3 = 0 (x +1)(x −3) = 0 x = −1 or x = 3 A(–1 ; 0) B(3 ; 0)
✔y = 0 ✔factors ✔x-values (3)
6.3
x = −1 + 3 or x = -b = -(-2) or fI (x) = 2x - 2 = 0 2 2a 2(1) x = 1 f(x) = x2 - 2x - 3 y = (1)2 - 2(1) - 3 or y = (x2 - 2x + (-1)2 ) - 3 - 1 y = -4 = (x - 1)2 - 4 y ≥ -4 or [-4 ; ∞]
✔x -value ✔ substitution/ completing the square ✔ answer (3)
6.4.1
MN: y = (x2 - 2x - 3) - (x + 1) = x2 - 3x - 4 6 = x2 - 3x - 4 0 = x2 - 3x - 10 0 = (x - 5)(x + 2) x = 5 or x = -2 OT = 2 or OT = 5 NA
✔ x2 - 3x - 4 ✔substituting y = 6 ✔values of x ✔ OT = 2 (4)
6.4.2
y = x +1 substitute x = −2 = (–2) + 1 = –1 N(–2 ; –1)
✔substituting x = –2 ✔answer (2)
6.5
OR
x2 − 2x − 3 = x + p x2 − 2x − 3 − x − p = 0 This equation will have equal roots, therefore: b2 − 4ac = 0 (-3)2 - 4(1)(-3 - P) = 0 9 +12 + 4p = 0 p = -21 4 y = x − 21 4
✔f ′(x) = 2x − 2 ✔2x − 2 =1 ✔ x = 3 /2 ✔ ✔answer (5)
OR
✔equating ✔equal roots ✔ substitution ✔simplification ✔answer (5)
6.6
k < - 21 4
✔answer (1)
[20]
QUESTION 7
7.1.1
✔0,088 and n = 16 4 ✔substitution into correct formula ✔answer (3)
7.1.2
✔ future value – amount including interest ✔ ✔answer (3)
OR
✔ R15 000 including interest – R100 000 ✔ on P and X in FV ✔method (3)
7.2.1
✔i = 0,105 12 ✔n = 240 ✔ substitution into correct formula ✔ answer (4)
7.2.2
= R5 259 229,61– R4 289 302,47 = R969 927,14
✔R14 975,70 in Pv -formula ✔✔n = 96 ✔ substitution into correct formula ✔ answer (5)
OR
✔ n = 144 in A-formula ✔n =144in Fv -formula ✔ R14 975,70 ✔ A – F ✔ answer (5)
[15]
QUESTION 8
8.1
✔x2 + 2xh + h2 − 5 ✔simplification ✔factorisation ✔ ✔2x (5)
OR
✔x2 + 2xh + h2 − 5 ✔simplification ✔factorisation ✔ ✔2x (5)
8.2.1
y = 3x3 + 6x2 + x − 4dy = 9x2 + 12x + 1 dx
✔9x2 ✔12x ✔1 (3)
8.2.2
y(x −1) = 2x(x −1) y = 2x(x - 1) if x # 1 x - 1 y = 2xdy = 2 dx
✔y(x −1) ✔2x(x −1) ✔y = 2x ✔answer (4)
[12]
QUESTION 9
9.1.1
g(x) = (x + 5)(x − x1 )2 20 = 5(x1 )2 x1 2 = 4 x1 2 = 2 g(x) = (x +5)(x − 2)2 g(x) = (x + 5)( x2 − 4x + 4) g(x) = x3 + x2 − 16x + 20
✔(x +5) ✔repeated root ✔x1 = 2 ✔g(x) = (x + 5)( x2 − 4x + 4) (4)
9.1.2
g(x) = x3 + x2 − 16x + 20 g′(x) = 3x2 + 2x − 16 3x2 + 2x - 16 = 0 (3x + 8)(x - 2) = 0 x = -8 or x = 2 3 R(-8 ; 1372 ) or R(-2,67;50,81) 3 27 P(2;0)
✔derivative ✔equating to zero ✔factors ✔co-ordinates of R ✔ co-ordinates of P (5)
9.1.3
g′′(x) = 6x + 2 g′′(0) = 2 ∴concave up
OR
g′′(x) = 6x + 2 6x + 2 = 0 x = − 1 /3 is the point of inflection ∴concave up
✔g′′(x) = 6x + 2 ✔g′′(0) = 2 ✔conclusion (3)
OR
✔g′′(x) = 6x + 2 ✔x = − 1 /3 ✔conclusion (3)
9.2
✔ y – intercept of a cubic graph ✔ point of inflection and stationary point, x = 3 ✔ concave up for x < 3and concave down for x > 3 (3)
[15]
QUESTION 10
10.1
AH = 3 HG 2
✔ answer (1)
10.2
Area of a parallelogram = base× ⊥height
✔ 2 /5 t ✔ 3 /5 (5 − t) ✔A(t) 6 /25 t2 + 6 /5 t ✔-12 /25 t + 6 /5 ✔answer (5)
[6]
QUESTION 11
11.1.1
75 = 16 807
✔✔ answer (2)
11.1.2
7 × 6 × 5 × 4 × 3 = 7! = 2520 2!
✔7 × 6 × 5 × 4 × 3 or 7! 2! ✔answer (2)
11.2
2×7×1= 14
✔✔✔2 × 7 × 1 (3)
[7]
QUESTION 12
12.1
P(A or B) = P(A) + P(B) 0,74 = 0,45 + y y = 0,29
✔ P(A or B) = P(A) + P(B) ✔substitution ✔answer (3)
12.2
Let the number of mystery gift bags = x The total number of bags = 4x
✔ 4x ✔ equating to 7 1187 ✔answer (6)
OR P(gift and gift) = P(gift at first draw) × P(gift at second draw) 7 = 1 × P(gift at second draw) 118 4 P(gift at second draw) = 7 ÷ 1 118 4 = 14 59 Therefore: P(gift at first draw) = 15 /60 And: 15 bags had mystery gifts inside
OR
✔¼ ✔ 1 × P(gift at 2nd draw) 4 ✔ 7 ÷ 1 P(gift at 2nd draw) 118 4 ✔14 59 ✔ 15 /60 ✔answer (6)
[9]
TOTAL: 150