Des { } indésirables

from tkinter import *

window = Tk()

def calcul():
    a=int(a_entry.get())
    b=int(b_entry.get())

    if b < 0:
        answer = ("y=(x", b, ") /", a)
        answer_entry.delete(0, END)
        answer_entry.insert(0, answer)

    else:
        answer = ("y=(x +", b, ") /", a)
        answer_entry.delete(0, END)
        answer_entry.insert(0, answer)

#creer une frame
frame = Frame(window, bg='#B8C0BF')

#Configuration de la fenetre
window.title("Réciproque d'une fonction")
window.geometry("600x400")
window.minsize(480, 360)
window.maxsize(740, 450)
window.iconbitmap("logo Sidramon.ico")
window.config(background='#B8C0BF')

#Titre
label_title = Label(frame, text="Calculer la réciproque d'une fonction", font=("Arial", 22), background=('#B8C0BF'))
label_title.pack()

#Bouton
bouton = Button(frame, text=("Lancer"), font=("Arial", 14), fg=('white') ,bg=('#B8C0BF'), command=calcul)
bouton.pack(pady=20, padx=12, side=RIGHT)
frame.pack()

#valeur de a
valeur_a = Label(frame, text="Valeur de a", font=("Arial", 17), background=('#B8C0BF'))
valeur_a.pack(side=TOP)
a_entry = Entry(frame, font=("Arial", 17), background=('#B8C0BF'))
a_entry.pack()

#valeur de b
valeur_b = Label(frame, text="Valeur de b", font=("Arial", 17), background=('#B8C0BF'))
valeur_b.pack(side=TOP)
b_entry = Entry(frame, font=("Arial", 17), background=('#B8C0BF'))
b_entry.pack(side=BOTTOM)

#reponse
answer_entry = Entry(window, font=("Arial", 17), background=('#B8C0BF'))
answer_entry.pack(side=BOTTOM, pady=80)

#menu
menu_bar = Menu(window)
file_menu = Menu(menu_bar, tearoff=0)
file_menu.add_command(label="Quitter", command=window.quit)
menu_bar.add_cascade(label="Menu", menu=file_menu)
window.config(menu=menu_bar)

#affichage
window.mainloop()