Cant multiply sequence by non-int type 'str'

[foxtreat]

i need it to be able to handle numbers like 2.31 and -12.9 for example so i set it as float if im correct
current code is this,it still fails

import math
print  ("Ax*2+Bx+C=0")
print ("what is your A?")
(a) = input('my a is: ')
print ("what is your B?")
(b) = input('my b is: ')
print ("what is your C?")
(c) = input('my c is: ')
print ("calculating")
float(a)
float(b)
float(c)
b2 = float(b)*float(b)
float(b2)
d = float(b2)-4*float(a)*float(c)
float(d)
sqd = math.sqrt(d)
x1a = float(-b)+float(sqd)
float(x1a)
x2a = float(-b)-float(sqd)
float(x2a)
ax2 = float(a)*2
float(ax2)
x1 = float(x1a)/float(ax2)
float(x1)
x2 = float(x2a)/float(ax2)
float(x2)
print ("your X1 is " + x1 +  "your X2 is") + x2
print ("your discriminant is" + d ) 

error here

Error:
Traceback (most recent call last):
  File "math.py", line 18, in <module>
    x1a = float(-b)+float(sqd)
TypeError: bad operand type for unary -: 'str'