Question

а)0,9x+0,4=13  б)(7+х)(5-х)=0

Answer 1

$a) 0,9x + 0,4 = 13 \ 0,9x = 13 - 0,4 \ 0,9x = 12,6 \ x = frac{12,6}{0,9} =14 \ x=14$

$b) (7+x)(5-x) = 0 \ 35-7x + 5x - x^2 = 0 \ -x^2-2x+35=0 \ x^2 + 2x - 35 = 0 \ D = 2^2 - 4 * (-35) = 4 - (-140) = 4 + 140 = 144 \ x_1_,_2 = frac{-2 б sqrt{D} }{2} = frac{-2 б sqrt{144} }{2} = frac{-2 б 12}{2} \ x_1 = 5 \ x_2 = -7$