I need help with this pls

the sum of interior angles of a triangle is =180

so

80 + 40 + x=180

120 + x= 180

x = 180 - 120

x = 60

60 is an acute angle

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hello from mrbilldoesmath!

answer:

a(n) - a(n-1) -3

discussion:

this ones a bit interesting. given a(n) = 5 - 3n consider this:

a(n-1) = 5 - 3(n-1)

          = (5 - 3n) + 3             => but a(n) = 5 - 3n, the first term

          = a(n)   + 3                 => subtract 3 from both sides

a(n-1) -3 = a(n)  

or

a(n) - a(n-1) -3

you,

mrb

27 +27 or 27times 2=54

the diffrence is 0