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Step-by-step explanation:
you have to put the picture of the polygon or we can't answer the question.
Hello :
the terme general is : an = a1 +(n-1)d
a11 = a1+(11-1)×5
a11 = -12+50
a11 = 38
<span>the sum of the first 11 terms is : S11 = (11/2)(a1+a11)
</span>S11 = (11/2)(-12+38)
S11 = 143
