51. Sepak bola

= 120 - ( basket + renang + bulu tangkis + catur )

= 120 - ( 36 + 20 + 18 + 23 )

= 120 - 97

= 23 orang

Sepak bola = 23/120. 360⁰

= 23.3 = 69⁰( b. )

52. 5x - 2y = 25 | ×3 | 15x - 6y = 75

2x + 3y = -9 | ×2 | 4x + 6y = -18

-------------------------------------------------- +

19x = 57

x = 3

Mencari y

2x + 3y = -9 3y = -9 - 6

2.3 + 3y = -9 3y = -15

6 + 3y = -9 y = -5

2x + 4y = 2.3 + 4(-5)

= 6 - 20 = -14( d. )

53. f(x) = ax² - bx - 5

f(-1) = a(-1)² - b(-1) - 5

0 = a.1 + b - 5

5 = a + b.....(1)

f(1) = a.1² - b.1 - 5

6 = a - b - 5

6 + 5 = a - b

11 = a - b......(2)

Eliminasi

a + b = 5

a - b = 11

--------------- -

2b = -6

b = -3

Mencari b

a + b = 5

a - 3 = 5

a = 5 + 3

a = 8

a + b = 8 - 3 = 5( d. )