A1 = - 15
a2 = - 15 - 10 = - 25
d = a2 - a1 = - 25 + 15 = - 10
a8 = a1 + 7d = - 15 - 7*10 = - 85
S8 - ?
S8 = (a1 + a8)/2* 8 = 4* ( - 15 - 85) = 4*(-100) = - 400
Y=Sin(x) * ln(x)
<span>y'=cos(x)*ln (x)+(Sin(x)) / x </span>
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{x+1>0⇒x>-1
{x+1<1/9⇒x<-8/9
x∈(-1;-8/9)