Mohon bantuannya no 15

14. Persamaan kuadrat x²+x + c = 0 --> a = 1, b = 1 , c = c
jika akar nya α dan β , maka
α+ β = -b/2 = - 1
α. β  = c/a = c
nilai α² + β² = 3

α²+β² = (α+β)² - 2(α β)
3=(-1)² - 2(c)
3 = 1 - 2c  --> 2c = 1 - 3  = - 2
c = -2/2 --> c = -1

15.
100 kg campuran pasir semen,  pasirnya 50 %
pasir = 30% x 100 kg = 50 kq
agar pasirnya 60 % , maka pasir ditambahkan = x kg

(50 + x )/(100+ x) = 60/100 = 3/5
5(50 + x) = 3(100 + x)
250 + 5x = 300 + 3x
5x - 3x = 300 - 250
2x = 50
x = 25 kg

16. Deret Geometri
u4 = 324 --> ar³ = 324 ,  dan  r = 3

u10 = ar⁹  = ar³. r⁶ = 324. 3⁶ = (324)(729) = 236.196

100 kg campuran --> 50% pasir
pasir = 50/100x100= 50 kg
semen = 100-50=50 kg
Dit = pasir = 60% (100+x) ---> x?
100 + x = semen + pasir
100 + x = 50 + 60/100(100+x)
50+x = 3/5 (100+x)
5(50+x)=3(100+x)
250+5x = 300+3x
2x = 50
x = 25
jawaban = 25kg d