Respuesta :

19)
you have 3 angles:
I: 5x
II: x+20
III: 2x

all three angles together are 180°
I+II+III=5x+x+20+2x=
8x+20=180
8x=160
x=20

insert x=20 into I, II, III:
I=5x=5*20=100
II=x+20=20+20=40
III=2x=2*20=40

20)
first line:
-8x-7>=-(5a-2)
to
-8x-7>=-5a-2
, but it should be
-8x-7>=-5a+2
instead

when the brackets were removed it was forgotten to invert all signs within it, (-2 -> +2)

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