c, 50 - 1 . ( -40 - 10 )
= 50 - 1 . -50
= 50 + 50
= 100
a, 25 - 34 - 25 + (-45) + 34
= ( 25 - 25 ) - (-34 + 34) + -45
= -45
b, -13 . 55 + 13 . 35 - 80 . 13
= 13 . -55 + 13 . 35 - 80 . 13
= 13.( -55 + 35 - 80 )
= 13 . -100
= -1300
\(x = {-b \pm \sqrt{b^2-4ac} \over 2a}\)