2xx-56x+180
2(xx-28+90)
axx+bx+c
a=1
b=-28
c=90
Multiply a and c:
1*90=90
Find multiples of ac that add up to b (d,e [ie de=ac, d+e=b]):
90=2*3*3*5
2*45
3*30
5*18
6*15
9*10
NONE add up to -28, use quadratic
Rewrite axx+bx+c into axx+dx+ex+c:
Factor sets of terms (ie axx+dx, and ex+c):
Combine like terms:
100+80, 99+81, 98+82....
To solve this one, subtract 50 from 180 and you'll have your answer.
It is: 126 plus 54 = 180
a + 3a + 5a = 180 9a =180 a = 20
It is: 97+83 = 180
It is: 157+23 = 180
It is 90+90 = 180
It is 134+46 = 180
180+72=252
87794 + 39357 + 180 + 439 = 127,770
180
120 + 60 = 180