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. )
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