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1) 6X+8=0 => 6x=-8 => x=-8/6
2) 3x+4=0 => 3x=-4 => x=-4/3
3) -12x+13=0 => -12x=-13 => x= 13/12
4) -x-4=0 => -x=4 =>x=-4 

a) f(x) = 3x² + 8x +2

(3x² + 8x + 2)' = 0

6x + 8 = 0

6x = -8

x = -8/6 = -4/3 = -1 целых 1/3

b) f(x) = -6x² + 13x - 1

( -6x² + 13x - 1)' = 0 

-12x + 13 = 0

-12x = -13

12x = 13

x = 13/12 = 1 ц 1/12

с) ) f(x) = 3/2x² + 4x - 1

( 3/2x² + 4x - 1)' = 0

3x + 4 = 0

3x = -4

x = -4/3 = 1 ц 1/3

d)  f(x) = -0.5x² - 4x + 0.1

(-1/2x² - 4x + 0.1)' = 0

-x -4 = 0

-x = 4

x = -4