Bagaimana anda graf f (x) = x ^ 5 + 3x ^ 2-x menggunakan nol dan tingkah laku akhir?

Bagaimana anda graf f (x) = x ^ 5 + 3x ^ 2-x menggunakan nol dan tingkah laku akhir?
Anonim

# "Mula-mula kita mencari nol" #

# x ^ 5 + 3 x ^ 2 - x = x (x ^ 4 + 3 x - 1) #

# x ^ 4 + 3 x - 1 = (x ^ 2 + a x + b) (x ^ 2 - a x + c) #

# => b + c-a ^ 2 = 0, #

# "" a (c-b) = 3, #

# "" bc = -1 #

# => b + c = a ^ 2, "" c-b = 3 / a #

# => 2c = a ^ 2 + 3 / a, "" 2b = a ^ 2-3 / a #

# => 4bc = a ^ 4 - 9 / a ^ 2 = -4 #

# "Nama k = a²" #

# "Kemudian kami mendapat persamaan padu berikut" #

# k ^ 3 + 4 k - 9 = 0 #

# "Pengganti k = r p:" #

# r ^ 3 p ^ 3 + 4 r p - 9 = 0 #

# => p ^ 3 + (4 / r ^ 2) p - 9 / r ^ 3 = 0 #

# "Pilih r supaya 4 / r² = 3 => r =" 2 / sqrt (3) #

# "Kemudian kita dapat" #

# => p ^ 3 + 3 p - (27/8) sqrt (3) = 0 #

# "Pengganti p = t - 1 / t:" #

# => t ^ 3 - 1 / t ^ 3 - (27/8) sqrt (3) = 0 #

# => t ^ 6 - (27/8) sqrt (3) t ^ 3 - 1 = 0 #

# "Pengganti u = t³, maka kita mendapat persamaan kuadrat" #

# => u ^ 2 - (27/8) sqrt (3) u - 1 = 0 #

#disc: 3 * (27/8) ^ 2 + 4 = 2443/64 #

# => u = ((27/8) sqrt (3) pm sqrt (2443) / 8) / 2 #

# => u = (27 sqrt (3) pm sqrt (2443)) / 16 #

# "Ambil penyelesaian dengan tanda +:" #

#u = 6.0120053 #

# => t = 1.8183317 #

# => p = 1.2683771 #

# => k = 1.4645957 #

# => a = 1.2102048 #

# => b = -0.50716177 #

# => c = 1.9717575 #

# x ^ 4 + 3 x - 1 = (x ^ 2 + a x + b) (x ^ 2 - a x + c) #

# "Jadi akarnya adalah" #

#x = (-a pm sqrt (a ^ 2-4 * b)) / 2 #

# => x = -0.6051024 pm 0.93451094 #

# => x = -1.53961334 "OR" 0.32940854 #

# "Dan" #

#x = (pm pmrt (a ^ 2-4 * c)) / 2 #

# => x = "tidak nyata sebagai" a ^ 2-4 * c <0 #

# "Jadi kita mempunyai tiga sifar untuk persamaan kuintik asal kita:" #

#x = = -1.53961334 "ATAU" 0 "ATAU" 0.32940854 #

# "Tingkah laku akhir adalah" #

#lim_ {x -> - oo} = -oo ", dan" #

#lim_ {x -> + oo} = + oo. "#

# "Jadi kami ada" #

# -oo "………" -1.53961334 "………" 0 "………." 0.32940854 "…….. "+ oo #

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